
class _JHLxa_o 

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COPYRIGHT DEPOSIT. 



STEAM BOILERS 



A PRACTICAL AND AUTHORITATIVE DISCUSSION OF BOILER 
DESIGN AND CONSTRUCTION, AND THE DEVELOP- 
MENT OF MODERN TYPES 



REVISED BY 

ROBERT II. KUSS, M. E. 

CONSULTING MECHANICAL ENGINEER 

FORMERLY SALES MANAGER, EDGE MOOR IRON COMPANY, CHICAGO 

AMERICAN SOCIETY OF MECHANICAL ENGINEERS 



ILLUSTRATED 



AMERICAN' TECHNICAL SOCIETY 

CHICAGO 

1919 






Copyright 1917, 1919 

BY 

AMERICAN TECHNICAL SOCIETY 



Copyrighted in Great Britain 
All Rig-hts Reserved 



If. </6 



od 



i7 1919 



ICI.A5 12652 



INTRODUCTION 

A STEAM boiler, although sometimes called "the heart of the 
plant", is really a dull and uninteresting machine to the 
average man. If one were to visit a big power plant, he would 
probably be first ushered into a clean engine room and shown the 
Corliss engine with its trim and stately lines or the stocky steam 
turbine of apparently simpler construction, depending upon what 
kind of a prime mover the plant possessed. At first thought the 
uninitiated layman might think that he had seen the best part of 
the plant; the wise man, however, would know that there was 
another power behind this mechanical throne and he would ask 
to be shown to the boiler room. Here he would find a long fine of 
boilers trembling with the energy pent up within them and with 
the fires underneath roaring most ominously. After seeing the 
mechanical stokers mysteriously carry the fuel to the fires with 
automatic regularity, watching the dials of a bewildering number 
of gages, and hearing the attendant discourse on the virtues of the 
superheaters which increase the temperature and pressure of the 
five steam, he would begin to have a wholesome respect for these 
dingy boilers and would realize more clearly their important function. 

<I Steam boilers are at least as old as the steam engine itself, 
and since the first boiler was conceived there have been many 
changes. In days when steam pressures did not exceed two pounds 
per square inch, certain methods of construction were permissible, 
but at the present time when steam pressures are often carried as 
high as 150 to 250 pounds per square inch, the strictest attention 
must be paid to every trifling detail of design and construction, 
in order to insure safety of the structure. Notwithstanding the 
enormous increase in the size of our industrial plants and the corre- 
sponding increase in the number of boiler horsepower required, the 
actual design of the modern boiler has not changed materially 
within the last few years. The sectional idea has been carried out 
to a point where a boiler plant is merely a combination of a number 
of units, the actual number of units being determined by the size 
of the boiler desired. 

<I The aim of this little volume is to cover in a very practical 
manner and yet with sufficient detail the methods of construction 
of the difficult types of boilers, the proper testing of the materials 
used, the methods of riveting and staying, and finally a careful 
discussion of the difficult types of stationary and marine boilers 
on the market. It is the hope of the publishers that the simplicity 
of style and the freedom of involved technical discussions will 
appeal to the readers. 




BOILER INSTALLATION WITH AMERICAN STOKERS AT PLANT OF KIRKMAN 
AND SON, BROOKLYN, NEW YORK 

Courtesy of Combustion Engineering Corporation, New York 



CONTENTS 

PART I 
CONSTRUCTION OF BOILERS 



PAGE 

BOILER MATERIALS 

Properties of metals 2 

Cast iron 2 

Wrought iron 2 

Steel 3 

Copper 4 

Brass 4 

Bronze. 4 

Physical tests 4 

Testing machines 7 

Standard testing regulations 8 

BOILER MANUFACTURING PROCESSES 

Riveted joints . 15 

Preparation for riveting 15 

Types of. 20 

Calking 25 

Welded joints 26 

Arrangements of plates and joints 27 

Manholes 33 

Location 33 

Frame construction 33 

Handholes 34 

Stays 34 

Necessity of staying flat surfaces 34 

Simple stay rod 35 

Gusset stay 36 

Diagonal stays 36 

Riveted stay bolts 37 

Stiffening angles 38 

Load on stay bolts 42 

Areas of segments of heads to be stayed 42 

Boiler tubes and flues 42 

Spacing of tubes 42 

Tube holes and ends 46 

Types of tubes 47 

Methods of expanding tubes 47 

Stay tubes 48 

Furnace flues 49 



CONTENTS 

PAGE 

BOILER REQUIREMENTS 

Factors in designing boilers 50 

Boiler horsepower 51 

General requirements. 51 

Water evaporation per pound of fuel 53 

Boiler rating 53 

Steam space 54 

Heating surface 55 

Allowable pressure 56 

Furnace flues 57 

Boiler inspection during manufacture 57 



PART II 
TYPES OF BOILERS 



MODERN FLUE BOILERS 

Cornish hoiler 9 

Path of hot gases 9 

Taking care of expansion 10 

Lancashire boiler 11 

Horizontal — two-flue — internally-fired 11 

Galloway boiler m . 12 

Horizontal — two-flue — internally-fired — Galloway tubes 12 

Two types 12 

FIRE-TUBE BOILERS 

Common horizontal type 14 

Single-flue boiler 14 

Multitubular boiler 14 

Vertical type 18 

Single-tube boiler i 18 

Multitubular boiler 19 

Internally-fired marine type 22 

Return-tubular boilers 22 

Through-tube boilers 29 

Fire-box type 29 

Locomotive boilers 29 

Stationary boilers 34 

Peculiar forms 34 

Return-tubular fire-box boiler 34 

Cochrane vertical boiler 35 

Shapley boiler 35 

Brady Scotch boiler 36 

Directum 38 



CONTENTS 

PAGE 

WATER-TUBE BOILERS 

Horizontal types 43 

Babcock and Wilcox 43 

Root t 46 

Worthington 49 

Edge Moor 49 

Heine 51 

Mosher 52 

Thorny croft-Marshall. 55 

Niclausse 56 

Vertical types 60 

Wickes 60 

Cahall 61 

Stirling 63 

Rust 65 

Bigelow-Hornsby 66 

Connelly 68 

Erie City 69 

Peculiar forms 72 

Hazelton or Porcupine 72 

Harrison 73 

MARINE BOILER TYPES 

Rectangular types 75 

Wet- and dry-bottom boilers 76 

Cylindrical types 77 

Marine water-tube boilers 77 

Comparison with cylindrical type 77 

Babcock and Wilcox boiler 79 

Standard boiler, U.S. wooden steamships 80 

Almy boiler 82 

Variations from standard types 84 

Launch boilers . . 85 

BOILER DESIGN 

Circulation 85 

Fire-tube boilers 85 

Water-tube boilers 86 

Importance of good circulation 87 

Effectiveness of heating surfaces 88 

Accessibility 90 

Replacement of tubes 91 

Shapes and sizes of tubes 92 

Plant features influencing boiler design 93 

Size of plant 93 

Stokers 94 

Water 94 

Fuel 94 

Available space 95 



PART I 

CONSTRUCTION OF BOILERS 



INTRODUCTION 

Essential Principles of Boiler Action. A steam boiler is a closed 
vessel used for generating steam from water by the application of 
heat. The boiler part of the steam-generating equipment must be 
clearly distinguished from the part having to do with the genera- 
tion of the heat which is offered to the boiler for absorption. The 
place or space in which heat is liberated from fuel by fire is called 
the furnace and, while closely associated with the art of steam 
generation, does not, in this paper, form an essential part of the 
subject under treatment. However, boiler construction is influenced 
to a considerable degree by the conditions imposed by highly heated 
gases, and to this degree reference will be made to construction 
modifications to allow for expansion, pressure, etc. 

In actual practice boilers are only partly filled with water, the 
remaining portion of the interior being filled with steam. More- 
over, facilities must be provided for supplying water to replace that 
which evaporates into steam; for the proper control and delivery of 
the steam generated; for the safe operation of the boiler by the aid 
of easy and reliable means for determining the height of the water 
therein; for the automatic release of steam to prevent excessive 
pressure; and for the removal of accumulated mud and other impuri- 
ties in the water without disturbing the continuity of operation. 
Discussion of these subjects and the related topics of boiler operation, 
furnace economy and control, etc., will be found in the book, "Boiler 
Accessories'', issued by the same publishers 

Scope of Work. The intention, then, of this article is to present 
an explanation of the characteristics of boiler construction without 
any attempt to meet conditions imposed by special branches of 
steam-generating service, as, for instance, locomotive practice, the 
thought being that the principles of construction, if worthy, must 
under all circumstances be preserved. 



2 CONSTRUCTION OF BOILERS 

In accordance with this intention, three elements of prime 
importance will be considered; namely, materials, designs, and 
ivorkmanship. It must be understood that these elements are 
closely associated. To illustrate, there are many designs which, 
because of the excellent materials and workmanship, are service- 
able and reliable, but which with inferior material and workman- 
ship would not be safe construction. Likewise, it is feasible and 
right to use certain kinds of materials in certain places and parts to 
which they are adapted, but which are not to be considered in other 
places and parts. 

Finally, it is not possible to lay down a course of boiler con- 
struction which could be universally adopted; the design must be 
modified and adjusted to meet the facilities of the shop in which 
the boiler is made. 

BOILER MATERIALS 

PROPERTIES OF METALS 

The materials of which boilers are constructed are exposed to 
conditions which weaken them and thus shorten the life of the 
boiler. Among these conditions are corrosion, both external and 
internal, high pressure, and expansion and contraction, due to 
varying temperatures and pressures. 

Cast Iron, Cast iron was the material of which the earliest 
forms of boilers were made but, on account of its low tensile strength 
and unreliable nature, it is now but little used, except for small 
parts of water-tube boilers, and sometimes for the ends of low- 
pressure cylindrical boilers, and for fittings. It resists corrosion but, 
on account of its unreliability and brittleness, the parts must be 
made thick and therefore heavy. 

Wrought Iron. Wrought iron, as late as 1870, was the principal 
material used for boiler plates. It is a pure iron prepared from 
pig iron by a process called puddling, described in "Metallurgy". 
Wrought iron is well adapted for use in boiler construction, as it is 
strong, tough, and fibrous, and combines high tensile strength with 
ductility and freedom from brittleness. When the properties men- 
tioned are well combined, wrought iron will resist stresses due to 
unequal expansion. Boiler fastenings, stays, and other parts made 



CONSTRUCTION OF BOILERS 

TABLE I 
Specifications for Chemical Composition of Open=Hearth Steel 



Element 


Flange Steel 


Fire-Box Steel 


BoiLER-RlYET 

Steel 


Manganese, per cent 
Phosphorus, per cent i . • i 
Sulphur, maximum per cent 


0.30 to 0.60 

0.04 
0.05 

0.05 


0.30 to 0.50 

0.035 
0.04 

0.04 


0.30 to 0.50 

0.04 
0.04 

0.045 



by welding are sometimes made of wrought iron. It is customary 
to consider that a bar loses about one-quarter of its strength by 
welding, although it is often stronger in the weld, owing to the 
working of the metal during the welding process. 

Steel. Steel has entirely displaced iron for boiler-shell work. 
Boiler steel is made by the open-hearth process, and contains for 
ordinary thicknesses of 1 or lj inches 0.25 per cent carbon, while 
thinner plates of £ inch should not contain over 0.15 per cent carbon. 
Larger percentages of carbon, while accompanied by an increase in 
tensile strength, lessen the ductility. The following properties show 
steel to be the best boiler material at present : great tensile strength, 
ductility, homogeneity, toughness, freedom from blisters and inter- 
nal unsoundness. Blisters and unsoundness are faults sometimes 
met with in wrought-iron plates. 

Chemical Composition. Open-hearth steel comes in three grades 
suitable for boiler use; viz, flange, fire-box, and boiler-rivet. It 
is customary to stipulate the requirements as to chemical compo- 
sition, as in Table I. 

The percentages given show that a very small amount of the 
steel is made up of matter other than iron; these small amounts, 
however, have a striking influence on the relative ductility, tough- 
ness, and tensile strength of the steel. 

To determine whether the boiler material conforms to any 
requirement such as given, a chemical analysis must be made. 

All steel ingots coming from the same ladle, as prepared by the 
open-hearth process, are not of uniform or homogeneous structure, 
different parts of the ladle producing steel of the three different 
grades mentioned. The position of the several grades of steel in 



4 CONSTRUCTION OF BOILERS 

the ladle is, of course, known by experiment and experience, and, 
as will be explained hereafter, there is no sharp line of demarcation 
between flange steel and fire-box steel, or between fire-box steel 
and boiler-rivet steel. 

Copper. Copper in many respects is superior to wrought iron 
for boiler construction. It is homogeneous, resists oxidation (the 
corrosive action of most feed waters), and incrustation. It is more 
ductile and malleable, and is a better conductor of heat, which not 
only gives it a higher evaporative usefulness, but also enables it to 
last longer under the intense heat of the furnace. Its disadvantages 
are its low tensile strength (about 30,000 pounds per square inch) 
and its decrease of strength with an increase of temperature. In 
heating from the freezing point to the boiling point it loses 5 per 
cent of its strength, and at 550 degrees F. it has lost about one- 
quarter of its strength at freezing point. For these reasons, and on 
account of its high price, it is now seldom used in boiler work except 
in very special places. 

Brass. Brass is an alloy of copper and zinc in which the pro- 
portions vary considerably. Red brass is better and more expensive 
than yellow brass as it contains a larger percentage of copper. 
Brass is used for valves, gages, and other fittings. Internal feed 
and other piping is preferably made of brass, as it resists corrosion 
and can be kept free of scale incrustation. 

Bronze. Bronze is an alloy of copper and tin, and is advanta- 
geously used for valves and seats of valves where the wear is great. 

PHYSICAL TESTS 

In order to determine the strength and other qualities of the 
materials, specimens are tested, the results showing the ultimate 
tensile strength, elastic limit, contraction of area, and elongation. 
These quantities as well as the rules and terms used in the text may 
be the better understood by a careful study of the following def- 
initions. 

Definitions. Stress. The number of pounds of force applied 
per square inch is called the stress. If the piece is under direct 
tension or compression, the stress is considered uniformly distributed 
and is equal to the load divided by the area of the transverse sec- 



CONSTRUCTION OF BOILERS 5 

tion. Thus, if the section of the plate is 1" by ft" and the actual 
stress is 17,750 pounds, the stress per square inch is 

40,570 



.4375 



= 17,750 lb. (approx.) 



Ultimate Strength. The maximum stress a test piece will stand 
per square inch is called its ultimate strength. For ductile mate- 
rials the breaking stress is considerably less than the ultimate 
strength. That is, when the loads are gradually applied the total 
load will reach a maximum, and then the metal stretches so that at 
the moment of rupture the load is much less than the maximum. 
The strength of iron and steel depends somewhat upon the rate at 
which the load is applied; the more rapid the application the higher 
the stress as recorded by the scale beam. 

Strain. Strain is the stretch per unit of length of the test 
piece when in tension. If the original length is L, and the stretch 
or elongation is B, the strain becomes 

§-■ 

Elastic Limit. When testing a piece, at first the stress and 
strain are proportional. The point at which the strain or stretch 
begins to increase more rapidly than the stress is called the elastic 
limit. This limit is not definite; it can be determined approximately 
only. A load greater than the elastic limit will produce a permanent 
elongation. 

Stretch Limit. The stretch limit is the stress at which the scale 
beam of the testing machine will fall while the straining head is at 
rest. 

Reduction of Area. When a test piece ruptures, the area at 
that point is much less than the plate or bar before testing. This 
reduction shows the ductility of the material; it also shows the 
property of changing shape without actual rupture. This is impor- 
tant in boiler construction. 

Elongation. Ductile materials stretch before breaking. To 
measure the ultimate elongation, the two broken pieces are placed 
in a straight line with the broken ends in contact and the length 
between points is then measured. As the prick punch marks are 
made before testing, the elongation is easily determined. The ratio 



6 



CONSTRUCTION OF BOILERS 



£■ Ssri •Jans* - * - *-* ** 

8, or .234, or 23.4 per cent " k ' mate elon K="io n is 1{ + 

by -Est F^rir i p r rties ;' -"* ■* <» *>» 

when n„ d e r tensi f n . ThluSt "7™ *" "^ ir °" "» d ^ 
the unit elongations as abse" « ^ £? "Vt" "* ° rdi " ates »* 
"W elongation, as fonnd by tote Z I T"- "* m "^^ 
- * *- throngb ^r CS £ 

/Ofinnnn i m i 




F . - ^ ^ "nit elongations r e •/* ./<5 

curve, those shown in FiV i k • 

Since stress and elongX^e Zt f V *«* &Ver ^ **«* 
the eurve from the ^nto t t!77T " P t0 the dastIc ***• 
the elastie limit the 1 I*!' ^e W is a straight line. A 
increases rapidly. iCSe^T,. 8 ^^ and the eIon ^tion 
Piece breaks the s tr e s S 7s not to ^ ^ ^ at which the 
of the eurve indicates th po nfoX 7^ to J*»**». The end 
erties of various material It U ? T CmVGS sh ° W the P«V 
well defined but ean htuIlZ T *** ^ *"* Iimit is ^ 
be plotted from results of teste I r t h 7 ^ TheSe Curves «^ 
by the testing machine 7 "^ be drawn automatically 



CONSTRUCTION OF BOILERS 7 

Testing Machines. The simplest way to test a piece of iron 
bar or plate for tensile strength would be to suspend a bar vertically, 
fixing it firmly at the upper end and hanging weights on the other 
end until the bar is broken. This is a crude method, and in order 
that the elastic limit and elongation may be determined at the same 
time, testing machines are used. There are many kinds of testing 




Fig. 2. Standard Testing Machine 
Riehle Brothers Testing Machine Company, Philadelphia 



machines, adapted for various materials, but the general principles 
are the same. 

The testing machine consists of a frame and two heads, to which 
the ends of the test piece are fastened by wedges or other devices. 
By means of steam or hydraulic power one head is drawn away from 
the other for tensile tests. The pull is transmitted to a weighing 



8 CONSTRUCTION OF BOILERS 

device, usually levers and knife edges like the beam of an ordinary 
platform scale. In small machines the pull may be applied by a 
lever. 

Testing machines are made for all varieties of testing: tensile, 
compressive, and shearing strength; also for deflection of beams, and 
for strength of wood, cement, brick, and stone. Fig. 2 shows a 
Riehle testing machine designed for tensile and compressive tests of 
iron and steel. 

Standard Testing Regulations. While the principles of testing 
materials are simple it is essential that the methods of applying them 
be uniform and as practiced by engineers, so that the results may 
be comparable. For this reason regulations supported by engineer- 
ing societies have been enacted, not by legislation necessarily, but 
by the societies or boards themselves. These regulations have all 
the force of legislative enactments since they are observed by persons 
dealing with the subject. 

The essential features of all the rules pertaining to boiler steel 
and the testing of it are contained in the following rules which are 
essentially those of the American Society of Mechanical Engineers. 
For the complete list of rules, see those prepared by the Society 
and found in all engineering libraries. 



RULES FOR TESTING BOILER STEEL 

SECTION 1 

BOILER SHELL MATERIAL 

1. All materials used in the construction of boilers shall conform to the 
specifications hereunder given. 

2. Only the best quality of open-hearth steel shall be used. 

CHEMICAL COMPOSITION 

3. All steel shall conform to the following requirements as to chemical 
composition : 

(a) Chemical Limits: manganese, 0.30 to 0.50 per cent; phosphorus, 0.03 

per cent maximum; sulphur, 0.03 per cent maximum. 

(b) Analysis: To determine whether the material conforms to the require- 

ments specified, an analysis shall be made by the manufacturer from a 
test ingot taken during the pouring of each melt. A copy of this 
analysis shall be given, upon request, to the purchaser or his repre- 
sentative. 






CONSTRUCTION OF BOILERS 9 

(c) Check Analysis: A check analysis may be made by the purchaser at 
his own expense, from one or more broken tension-test specimens as 
selected by the inspector. Samples to be taken for check analysis, 
in the case of plates, by drilling through the entire thickness of the 
material, and in the case of bars by drilling or turning in such manner 
as to secure the sample to represent, as nearly as possible, the material 
lying midway between the central axis and the outside of the bar, 
care being taken to remove all scale, rust, grease, etc., so that no 
foreign matter shall be in the sample. This analysis shall conform 
to the requirement specified. 

PHYSICAL PROPERTIES AND TESTS 

4. Physical Properties. All bar steel and all shell plates and butt straps, 
which in service will be subject to full tension stress and used in pressure vessels 
not subject to the direct action of the fire or products of combustion, shall show 
physical properties as follows : 

(I) PHYSICAL PROPERTIES REQUIRED FOR BAR STEEL AND STEEL PLATES 

Tensile strength, per sq. in 55,000 to 65,000 lb. 

Elongation in standard S-in. specimen not less than 23 per cent 

Reduction of area not less than 50 per cent 

It is very desirable that all plates 1 inch and over in thickness intended for 
shell plates of boilers shall be annealed at the plate mill. 

(II) PHYSICAL PROPERTIES REQUIRED FOR STEEL PLATES EXPOSED TO 

FIRE OR PRODUCTS OF COMBUSTION 

Tensile strength, per sq. in 52,000 to 60,000 lb. 

Elongation in standard S-in. specimen not less than 25 per cent 

Reduction of area not less than 52 . 5 per cent 

All bars for rivets, stay bolts, and braces, and all steel which is to be welded 
for furnaces, tubes, and pipes entering into the construction of boilers or other 
pressure vessels, shall show physical properties as follows, and shall be known 
as extra soft steel. 

(III) PHYSICAL PROPERTIES REQUIRED FOR RIVETS, BRACES, TUBES, AND 

STEEL TO BE WELDED 

Tensile strength, per sq. in 45,000 to 55,000 lb. 

Elongation in standard S-in. specimen not less than 28 per cent 

Reduction of area not les3 than 55 per cent 

5. Homogeneity Tests. A sample taken from a broken tension-test speci- 
men shall not show any single seam or cavity more than \ inch long, in either 
of the three fractures obtained in the test for homogeneity, which shall be made 
as follows: 

A portion of the broken tension-test specimen is either nicked with a chisel 
or grooved on a machine, transversely, about y& i ncn deep, in three places 
about 2 inches apart. The first groove is made on one side, 2 inches from the 
square end of the specimen; the second, 2 inches from it on the opposite side; 
and the third, 2 inches from the last, on the opposite side from it. The specimen 
is then put in a vise, with the first groove about \ inch above the jaws, care 
being taken to hold it firmly. The projecting end of the test specimen is then 
broken off with a number of light blows of a hammer, the bending being away 



10 



CONSTRUCTION OF BOILERS 



from the groove. The specimen is broken at the other two grooves in the same 
manner. The object of this test is to open and render visible to the eye any 
seams due to failure to weld up or to interpose foreign matter, or any cavities 
due to gas bubbles in the ingot. After rupture, one side of each fracture is 









PARALLEL SECTION 






^ABOUTJ 




/ "to j "raj?. 


NOT LESS THAN 3" 

(4 


" 
















X 

< 




t 

AB0U1 
I 


■^ 


2 


I 


/" 


ETC, 




_ T 








about /a " 






, — _»» 





PIECE TO BE OF SAME THICKNESS AS THE PLATE 
Fig. 3. Steel Specimen for Tension Test 

examined, a pocket lens being used if necessary, and the lengths of the seams 
and cavities are determined. 



6. 

(a) 
(&) 



(c) 



W) 



w 

7. 
(a) 



Bend Tests. 

Cold-bend tests shall be made on the material as rolled. 

Quench-bend test specimens, before bending, shall be heated to a light 
cherry red as seen in the dark (about 1200 degrees F.), and quenched 
in water, the temperature of which is about 80 degrees F. 

Specimens for cold-bend and quench-bend tests from plates shall bend 
through 180 degrees without fracture on the outside of the 
bent portion, as follows: For material 1 inch and under in thickness, 
flat on itself; for material over 1 inch in thickness, around a pin, the 
diameter of which is equal to the thickness of the specimen. 

Specimens for cold-bend and quench-bend test of boiler-rivet steel shall 
bend cold through 180 degrees flat on themselves without fracture 
on the outside of the bent portion. 

Bend tests may be made by pressure or by blows. 

Test Specimens. 

Tension- and bend-test specimens for plates and brace bars, flat or 
square, shall be taken from the finished product, and shall be of the 



I 




Goge Length not less than 4- times dia -* 
With entorgecf ends parol let for a length not 



less than 4- i limes the diameter 

Fig. 4. Standard Test Piece for Rivets 

full thickness of material as rolled. Tension-test specimens shall be 
of the form and dimensions shown in Fig. 3. Bend-test specimens 
shall be \\ inches to 2 J inches wide, and shall have the sheared 
edges milled or planed. 



CONSTRUCTION OF BOILERS 



11 



(6) For tension tests, rivets will be tested to a gage length of not less than 
four times the diameter, as shown in Fig. 4. 
Rivets from each lot offered, selected by the inspector, shall stand the 
following tests: 

(1) Bend Tests. The rivet shanks shall bend cold through 180 degrees 

flat on themselves, as shown in Fig. 5, without fracture on the 
outside of the bent portion. 

(2) Flattening Tests. The rivet heads shall flatten, while hot, to a 

diameter 2\ times the diameter of the shank, as shown in Fig. 
6, without cracking at the edges. 

(3) Finish. Rivets shall be true to form, concentric, and free from 

injurious scale, fins, seams, and other defects. 

(4) Rejection. Rivets which fail to meet the requirements specified 

in (1) and (2) will be rejected and returned to the manufacturer, 
who shall pay return freight. 





Fig. 5. Section of Rivet 
Shank After Bend Test 



Fig. 6. Rivet Section 
After Flattening Test 



FINISH AND MARKINGS 

8. Variation in Oage. The thickness of each sheared plate shall not vary 
more than 0.01 inch under that ordered. 

9. The finished material shall be free from injurious defects, and shall have 
a workmanlike finish. 

10. All plates and other materials used in the construction of steam 
boilers and other pressure vessels shall be tested at the mill or place where such 
materials are manufactured, and the manufacturer shall make all tests and 
furnish such records of same as shall be required by these rules, and stamp each 
plate with the name of such manufacturer, where manufactured, and the heat 
number from which such plates were made, the tensile strength, and the thick- 
ness. Four such stamps shall be placed on each plate having an area of 25 
square feet or under, about 6 inches from the edges at diagonal corners, and one 
about the center of the plate, or as may be directed by the inspector, as desig- 
nated by the boiler maker in his order for the plates. Plates over 25 square 
feet area, shall have five such stamps, about 12 inches from the edge at the four 
corners, and one about the middle of the plate. 

Each head or plate to be flanged shall be distinctly stamped by the manu- 
facturers on both sides as directed by the purchaser of the material, or by the 



12 CONSTRUCTION OF BOILERS 

boiler maker, with the name of the manufacturers, place where manufactured, 
lowest tensile strength, and the thickness; stamps to be so located as to be plainly 
visible when the head is finished and in position in boiler or pressure vessel. 
11. Inspection and Rejection. 

(a) The inspector shall have free entry, at all times while work is being 

performed, to all parts of the manufacturer's works which concern 
the manufacture of the material ordered for boilers or other pres- 
sure vessels. The manufacturer shall afford the inspector, free of 
cost, all reasonable facilities to satisfy him that the material is 
being furnished in accordance with these specifications. All tests 
and inspections shall be made at the place of manufacture prior 
to shipment. 

(b) Material which, subsequent to the above tests at the mills and its 

acceptance there, develops weak spots, brittleness, cracks, or other 
imperfections, or is found to have injurious defects, may be rejected 
at the shop, and shall then be replaced by the manufacturer at 
his own cost. 

SECTION 2 

MISCELLANEOUS MATERIAL 

1. Shells, drums, butt straps, heads, combustion chambers, furnaces, or 
any plates that require staying or flanging, shall be of open-hearth steel as speci- 
fied in Section 1, Paragraphs 2, 3, 4, 5, and 6, of these rules. 

2. Tubes shall be made of seamless hot or cold drawn steel for water-tube 
boilers. Lap-welded steel tubes shall not be further used in new water-tube 
boilers nor in retubing old water-tube boilers. 

3. Rivets, stay bolts, and braces shall be of open-hearth extra soft steel, 
as specified in these rules. 

4. Cast steel for use in boilers and steam superheater mountings, manhole 
frames, steam pipe, fittings, side lugs, or any other parts of boilers or superheaters 
where cast steel is used, shall have the following chemical and physical properties: 

(a) Chemical Composition: The steel shall conform to the following 

requirements as to chemical composition: 

Phosphorus not over 0.05 per cent 

Sulphur not over 0.05 per cent 

(b) Chemical Analyses: To determine whether the material conforms to 

the requirements as to chemical composition specified in (a), an 
analysis shall be made by the manufacturer from a test ingot taken 
during the pouring of each melt. Drillings for analysis shall be 
taken not less than \ inch beneath the surface of the test ingot. 
A copy of this analysis shall be given to the purchaser or his repre- 
sentative. 

A check analysis of castings may be made by the purchaser from 
a broken tension or bend-test specimen, in which case an excess of 
20 per cent above the requirements as to phosphorus and sulphur 
specified in (a) will be allowed. If the specimen has been annealed, 
the drillings for analysis shall be taken not less than \ inch beneath 
the surface. 



CONSTRUCTION OF BOILERS 13 

(c) Tension Tests: The steel for castings shall conform to the following 

minimum requirements as to tensile properties: 

Tensile strength, lb. per sq. in 50,000 to 60,000 

Elongation in 2 in 22 per cent 

Reduction of area 30 per cent 

(d) Bend Tests: The test specimen shall bend cold through 120 degrees 

for soft castings and 90 degrees for medium castings, around a 1-inch 
pin, without fracture on the outside of the bent portion. Bend tests 
may be made by pressure or by blows. 

(e) Alternative Tests to Destruction: In the case of small or unimportant 

castings, a test to destruction on three castings from a lot may be 
substituted for the tension and bend tests. This test shall show 
the material to be ductile, free from injurious defects, and suitable 
for the purpose intended. A lot shall consist of all castings from 
the same melt, annealed in the same furnace charge. 

(/) Test Specimens: Test bars shall be attached to all castings weighing 
500 pounds or over, provided the design of the castings will permit. 
If the castings weigh less than 500 pounds or are of such a nature 
that test bars cannot be attached, two test bars shall be cast to rep- 
resent each melt; or the quality of the castings shall be determined 
by tests to destruction as specified in (e). All test bars shall be 
annealed with the castings they represent. The manufacturer and 
purchaser shall agree whether test bars can be attached to castings, 
and also on the location of the bars on the castings and the method 
of casting unattached bars. Bend-test specimens shall be 1 by § 
inch in section. 

(g) Number of Tests: One tension and one bend test shall be made from 
each melt. If any test specimen shows defective machining or 
develops flaws, or if a tension-test specimen breaks outside the gage 
length, it may be discarded; and the manufacturer and the pur- 
chaser or his representative shall agree upon the selection of another 
specimen in its stead. 

5. Cast iron for use in boiler mountings, steam-pipe fittings, side lugs, or 
any other parts of boilers where cast iron is permitted to be used, shall not have 
less than 20,000 pounds tensile strength. 

6. Cross pipes connecting the steam and water drums of water-tube 
boilers and cross boxes shall be of wrought or cast steel when the working pres- 
sure exceeds 125 pounds per square inch. 

7. Mud drums of water-tube boilers and all pressure parts over 2-inch 
pipe size, or equivalent cross-sectional area, on any boiler, shall be of wrought or 
cast steel when the working pressure allowed on the boiler exceeds 125 pounds 
,;age per square inch. 

8. Pressure parts of superheaters, attached to boilers or separately fired, 
shall be of wrought or cast steel. 

9. Boiler and superheater mountings, such as nozzles, cross pipes, steam 
pipes, fittings, valves and their bonnets shall be of wrought or cast steel when 
exposed to steam which is superheated over 80 degrees F. 

10. Water-leg and door-frame rings of vertical fire-tube boilers, 30 inches 
or over in diameter, shall be of wrought or cast steel, or wrought iron. A wrought- 



14 CONSTRUCTION OF BOILERS 

iron mud ring shall be used at the bottom in water legs of boilers, and this water 
leg shall not be formed by bending in the plates and riveting together at the 
edges. 

11. Water-leg and door-frame rings of locomotive type boilers shall be of 
wrought or cast steel, or wrought iron. 

SECTION 3 

STAMPING OF BOILERS 

1. In laying out shell plates, furnace sheets, and heads in the boiler shop, 
care shall be taken to leave at least one of the stamps, specified in Section 1, 
Par. 10, of these rules, so located as to be plainly visible when the boiler is com- 
pleted; except that the tube sheets of a vertical fire-tube boiler shall have a 
portion, at least, of such stamps visible sufficient for identification when the 
boiler is completed. 

2. Each boiler shall conform in every detail with these standard rules, and 
shall be distinctly stamped by a member of the state boiler department, or an 
inspector holding a certificate of competency as an inspector of steam boilers, 
and who is not, directly or indirectly, interested in the manufacture or sale of 
steam boilers, but in the employ of an insurance company authorized to insure 
boilers in this State. Each boiler shall be stamped by the builder, in the pres- 
ence of the inspector, with a serial number and with the name of the builder 
either in full or abbreviated and the builder shall submit a facsimile of his pro- 
posed style of stamping to the state boiler department for approval. The height 
of letters and figures used in stamping shall not be less than I inch. 

3. In numbering serially, each builder shall commence with the number 
1 and continue numbering in consecutive order. 

4. Location of Stamps. The location of stamps is to be as follows: 

(a) On horizontal return-tubular boilers — on the front head, above the 

central rows of tubes. 

(b) On horizontal flue boilers — on the front head, above the flues. 

(c) On locomotive type or star water-tube boilers — on the furnace 

end, above the handhole. 

(d) On vertical fire-tube and vertical submerged-tube boilers — on the 

shell, above the furnace door. 

(e) On water-tube boilers, Babcock and Wilcox, Stirling, Heine, and 

Robb-Mumford standard types — on a head above the manhole 

opening, preferably on the flanging of the manhole opening. 
(/) On vertical boilers, Climax or Hazleton type — on the top head. 
(g) On Cahall or Wickes vertical water-tube boilers — on the upper 

drum, above the manhole opening. 
(h) On Scotch marine boilers — on the front head, above the center or 

right-hand furnace. 
(i) On Economic boilers — on the rear head, above the central rows of 

tubes. 
(j) For other types and new designs — in a location to be approved by 

the board of boiler inspectors. 

5. The standard stamp and the boiler builder's stamps shall not be cov- 
ered by insulating or other material. 






CONSTRUCTION OF BOILERS 15 

6. All boiler shops in which boilers are constructed for installation in this 
State shall be open to the members of the state boiler department and inspectors 
holding certificates of competency as inspectors of steam boilers, at all reason- 
able hours, for inspection of material, methods of manufacture, workmanship, 
and testing. 

BOILER MANUFACTURING PROCESSES 

Shop Equipment. As has been previously stated, the design an 
engineer may submit for boiler construction is dependent upon the 
facilities offered by the shop in which the boiler is built. 

Boiler shops are equipped with the following tools: plate 
rolls, plate planers, shears, drill presses, punches, countersinking 
machines, flanging machines, hydraulic and steam riveters, and a 
compressed-air system for operating pneumatic machines, such as 
calkers and chippers. They also have machine shops for doing 
such machine work as is required for fittings, furnace fronts, etc., 
and a system of cranes for handling and transporting material. 
In connection with the above is a storeroom of sufficient size, a 
forge shop, and an engine and boiler for supplying the shop with 
the power necessary to operate it. 



RIVETED JOINTS 

PREPARATION FOR RIVETING 

Drilled vs. Punched Rivet Holes. In boiler work the drilling 
of rivet holes is gradually displacing punching. Punching is cheaper 
than drilling, but it is more injurious to the plates and not so accu- 
rate. • It is easy to see that drilling rivet holes, even if twenty are 
being drilled at once, is done with less strain on the plates than 
when done by a punch. 

Force Required for Punching. The force required to punch a 
plate gives the best idea of the harm done to the plate. Experiment 
shows that the resistance of a plate to punching is about the same 
as its resistance to tensile tearing. Suppose this to be 50,000 pounds 
per square inch; then the force required to punch the plate is the 
area cut out times the shearing strength, or dXirXtX 50,000. 

jT = rfX7rX/X50,000 
in which d is diameter in inches and t is thickness in inches. 



16 CONSTRUCTION OF BOILERS 

For a hole f inch in diameter in a |-inch plate, the force will be 

|X3.1416X^X50,000 = 58,900 lb. 
A good, ductile plate is but little injured by punching, but 
if of a hard, steely nature, it is likely to be seriously injured. For 
this reason wrought-iron plates are usually punched and steel plates 
are drilled. On the whole, a drilled plate is somewhat stronger than 
a punched plate for any kind of joint with plates of like thickness. 
Reamed Holes. Some boiler makers punch the rivet holes 
smaller than the desired size and then ream them out. By this 
process most of the injured metal around the holes is cut away. 
Annealing. Another method to overcome the injurious effects 
of punching is to anneal the plate. The ordinary process of 
annealing consists of heating the plate to red heat and then allowing 
it to cool slowly. By this means, hard and brittle iron or steel is 
made soft and tough. While the metal is hot, the surface becomes 
oxidized. For most purposes this oxide scale is not harmful, but 
in some cases it must be removed. As this is expensive, a process 
of annealing in illuminating gas has been devised. The action of 
the gas is to reduce the oxide without altering the properties of the 
piece. The results obtained from annealing depend upon the kind 
of iron or steel, the temperature to which it is raised, and the rate 
of cooling. It is a great advantage to all steel of over 64,000 pounds 
per square inch in tensile strength, but softer steels are little better 
for the process. 

The shops that do the best boiler work proceed in the following 
manner: 

Standard Practice. Holes for rivets in flat plates are drilled 
while plates are "tacked" together by bolts, the drills being guided 
by small punched holes in the upper plate only. Plates are taken 
apart after drilling, scraped free of all burrs and chips, and reassem- 
bled for riveting. 

Shells are rolled in cylinders and assembled for riveting, and the 
plates and butt straps are drilled in place rg inch larger than the rivet. 
The foregoing construction insures true holes, and the holes in 
both plates must match with absolute accuracy, thus avoiding all 
necessity for the use of a driftpin, which so often produces injurious 
strains which materialize only after the boiler has been placed in 
service. 



CONSTRUCTION OF BOILERS 



17 



It is important that the burrs be removed from both edges 
around the rivet holes of every sheet, for if not done, the metal of 
the burr will form a shallow sharp ring around the rivet when it is 
driven, or crowd between the plates, thus preventing a tight, flush 
joint between adjacent sheets. 








Fig. 7. 



BCD 
Types of Rivet Heads Before and After Being Driven 



Forms of Rivets. Rivets are forged from round iron or mild 
steel bars, with a cup- or pan-shaped head. The cylindrical part, 
called the shank, is a little smaller than the hole in which it enters 
and has a slight taper. Fig. 7 shows common forms of rivets before 
and after being driven. As rivets are not as reliable in tension as 




Fig. 8. Diagram of Three Forms of Rivets with Dimensions. Referred 
to in Table II 



>w^d ( B ) 



T 
_JL 








in shear, they are used mainly at right angles to the pulling force. 
If the stress is parallel to the axis, bolts may be used, since they are 
strong in tension. The shearing strength of steel rivets is about 
45,000 pounds per square inch, and of iron rivets about 40,000 
pounds per square inch. Steel rivets are often used with steel 



18 



CONSTRUCTION OF BOILERS 

TABLE II 
Dimensions of Rivets 



DlAMETEK 
OF 

Rivet 


Cone Head 
A 


Countersunk 
B 


Button Head 
C 


D 


E 


F 


G 


E 


G 


E 


G 


5 
8 
11 
16 
3 
4 
7 
8 
1 


ItV 

11 

li 
1* 

If 


19 
32 
21 
32 
23 
32 
13 
16 
15 
16 


9 

16 
39 
64 
21 
32 
3 
4 
27 
32 


ItV 

1* 

u 

-L8 

1 £ 


9 
32 

5 
16 

3 

8 
7 
16 

1 
2 


ItV 

H 
H 

ItV 
If 


7 
16 

1 

2 

9 
16 

4 
3 

4 



plates, but many boiler makers prefer to use iron rivets in all 
cases. 

Three types of rivets in use are shown in Fig. 8, Table II, giving 
the dimensions. 

Methods of Driving Rivets. Hand Method. Formerly all 
boiler joints were riveted by hand, but now most riveting is done 
by machines, except those rivets to which a machine cannot be 
applied. If done by hand, the red-hot rivet is inserted in the hole, 
and the second head formed by two riveters working with hammers. 
This head is either made conical by the hammers alone or finished 
with a cup-shaped die called a "snap". The latter is the more usual 
method. The disadvantages of hand riveting are slowness and a 
tendency to form a shoulder before the rivet fills the hole. 

Machine Method. Machine riveting is preferable to hand rivet- 
ing, as the work is done better, faster, and more accurately; the 
pressure coming gradually on the entire rivet, compresses it com- 
pletely into the hole before the head is formed. Before riveting, 
care should be taken that the plates are close together, so that a 
shoulder will not be formed between the plates and prevent a good 
joint. Rivets should always be put in while red-hot, for in this 
condition they are more easily worked, and when they cool they 
contract, nipping the plates together in a tight joint. 

Hydraulic riveting is more gradual, and is generally preferred 
to steam riveting. The pressure from the steam riveter often 
comes as a sudden blow and does not allow time for the rivet to 
completely fill the hole. In either case the rivet should be held 
under pressure until black. 



CONSTRUCTION OF BOILERS 19 

Use of Rivets with Countersunk Heads. It is sometimes desir- 
able to rivet with a countersunk head; that is, the rivet does not 
project above the plate. The countersunk head is formed by 
hammering down the end of the rivet into the countersink in the 
plate. This form is shown at D, Fig. 7. This joint is often used in 
shipbuilding and in boiler making when it is necessary to attach 
mountings. It should always be avoided, if possible, on account 
of its weakness, and especially when the pulling force acts in the 
direction of the length of the rivet, as the head has a very insecure 
hold and is likely to be pulled through the hole. 

Temperature of Rivets for Driving. Steel rivets should not be 
heated to a white heat, as iron rivets are, but to a bright cherry red, 
for if heated beyond this point they will burn. The fire in which steel 
rivets are heated should be kept thick, and the draft moderate. 

Shaping Butt Straps. Butt straps should be bent into true 
parts of cylinders of a radius equal to that of the finished boiler drum. 
Under no circumstances is it considered good practice to bend butt 
straps by a series of "kinks" to give them an approximate true bend. 
The edges of plates should be bevel planed to facilitate calking. 

Flanging. The construction of practically every design of 
boiler manufactured from sheets requires the flanging of some of 
the parts. This is true of water-tube as well as fire-tube boilers. 
No other part of boileF work, when properly done, requires so much 
careful design and workmanship as flanging, although in many shops 
this would not appear to be true. As a first principle, the sheet 
should not be flanged so that the radius of curvature is small, espe- 
cially where there is a possibility of "breathing" action being con- 
centrated at the flanged portion. By "breathing" is meant the 
periodic change of shape between the flat or main portion of the 
sheet and its flanged edge, due to changes of pressure or to the 
deformation of other portions of the boiler exerting stresses upon the 
flanged section. 

The next item, and one fully as important, is that the flanged 
sheet must be uniformly heated to a cherry-red temperature and 
the work completed before this temperature is lost by radiation. 
A second heating sets up local stresses which can be only partly 
removed by annealing. Rather than heat the sheet more than 
once, some other form of design must be selected if necessary. 



20 CONSTRUCTION OF BOILERS 

If it is impracticable to heat an entire metal piece for a small 
flange, as, for instance, at the end of an internal furnace of a Scotch 
boiler, the heat is applied locally, but the whole must be carefully 
annealed after the flanging is done. 

Some boiler shops perform all simple flange work without 
heating the sheets. It may be stated that this practice should 
always be discouraged when intended for use in constructing high- 
pressure boilers. Another practice which is in disfavor is hammer- 
ing by hand; in fact flanging by any other process than by the 
use of suitable machinery should be avoided in building high-pressure 
boilers. 



TYPES OF RIVETED JOINTS 

Efficiency of a Joint. It is obvious that a plate is weakened 
by removing the metal of rivet holes. It is customary to speak of 
the strength of a riveted joint in terms of the percentage of the 
strength preserved of the original plate; the ratio of the joint strength 
to that of the original sheet, expressed in decimals, is called the 
efficiency of the joint. Riveted joints may fail in several ways: 
(1) By shearing the rivets. (2) By tearing the plate at the 
reduced section between the rivets. (3) By crushing the plate or 
rivets where they are in contact. (4) By cracking the plate 
between the rivet hole and the edge of the plate. As in practice 
the lap can always be made sufficiently wide, a joint need never 
fail in the last-named way. 

Classification. The names given to the several kinds of joints 
are descriptive, as, for instance, the term "lap joint' ' is applied to a 
joint in which the edges of the sheet to be joined overlap. A "butt 
joint" is the name given to a joint in which the edges of the joined 
sheet do not overlap but meet each other edge on, while the fasten- 
ing is accomplished by the use of straps which overlap the edges 
to be united. 

The number of rows of rivets parallel to the length of the joint 
are expressed in the terms "single", "double", "treble", etc. In 
butt-joint seams the word designating the number of rows of rivets 
refers to the number of rows on one side of the joint only; thus a 
treble-riveted butt joint has actually six longitudinally rows of 
rivets, three on each side of the meeting line of the joined sheets. 






CONSTRUCTION OF BOILERS 



21 



Lap Joints. Circumferential or girth seams are usually lap 
joints since the tendency to rupture at these seams is only one-half 
as great as at the longitudinal 
seams. 

Longitudinal lap seams are 
usually double riveted, and for 
higher pressures, treble riveted. 
Fig. 9 shows the most simple form 
of this joint and is called a single- 
riveted lap joint. Double-riveted 
lap joints may have the rivets 
arranged as shown in Figs. 10 and 
11. The former joint is called a 
double-riveted lap joint with chain riveting, and the latter a double- 
riveted lap joint with staggered riveting. The staggered riveting 
is a little weaker than the chain, but the joint is usually tighter and 
less lap is required. 

Efficiency. The efficiency of lap joints depends upon the pitch 
and diameter of the rivets, the thickness of the plates, and the 





Fig. 9. Single- Riveted Lap Joint 




Fig. 10. Double-Riveted Lap Joint, 
Chain Riveting 



Fig. 11. Double-Riveted Lap Joint, 
Staggered Riveting 



number of rows. The efficiency is also somewhat altered if the 
plates are drilled instead of punched. As there are so many condi- 
tions we can give only rough average efficiencies. 

Lap joint, single riveted, efficiency about 56% 
Lap joint, double riveted, efficiency about 70% 
Lap joint, treble riveted, efficiency about 72% 

It is well to remember that the efficiency figures are calculated 

without reference to the creation of an eccentric load on the sheets 

and the rivets. The true efficiency figures are appreciably less than 



22 



CONSTRUCTION OF BOILERS 

TABLE III 
Proportions of Riveted Lap Joints 









Pitch, 


[nches 


Efficiency 


Thickness 
of 


Diameter 
of 


Diameter 
of 
















Plate 


Rivet 


Hole 


Single 


Double 


Single 


Double 


(In.) 


(In.) 


(In.) 


Riveted 


Riveted 


Riveted 


Riveted 


1 

4 


5 

8 


n 

16 


2 


3 


.66 


.77 


5 
16 


11 

16 


3 
4 


^16 


3J 


,64 


.76 


3 

8 


3 
4 


13 

16 


2| 


31 


.62 


.75 


7 
16 


13 
16 


7 
8 


^16 


3f 


.60 


.74 


1 
2 


7 
8 


15 
16 


2i 


3| 


.58 


.73 



those calculated, for it is impossible when using lap joints to avoid 
the tendency of the sheet to pull into a curved line of a radius equal 
to that of the cylinder of which it forms a part. 

Table III gives the proportions of riveted lap joints for average 
practice in boilers of up to about 150 pounds pressure. 

The probable efficiency of joints may be calculated by mathe- 
matics, but the actual efficiency can be obtained only by means of 
the testing machine. In testing, a piece of uncut plate, the size of 
which depends upon the capacity of the machine, is first tested. 
Then a portion of the joint of approximately the same size is tested. 
The ratio of the breaking strength of the joint to that of the uncut 
plate is its efficiency. 

Butt Joints. Longitudinal seams, except for small diameters, 
are almost always made with butt joints. These joints are seldom 
single riveted because as such they are not much stronger than a 
double-riveted lap joint and are more expensive. If, however, they 
are made with double butt straps and double or treble riveted, the 
joint shows a high efficiency. The two butt straps may be of the 
same width or the inner may be wider than the outer. Fig. 12 shows 
a double-riveted butt joint with two butt straps. A treble-riveted 
butt joint is shown in Fig. 13. 

Efficiency. The following are approximate efficiencies: 

Butt joints, single riveted, efficiency about 65% 
Butt joints, double riveted, efficiency about 75% 
Butt joints, treble riveted, efficiency about 85% 

Butt straps should be at least five-eighths the thickness of the 
shell plates. In all of the butt joints illustrated the outer strap is 



CONSTRUCTION OF BOILERS 



23 



made narrower than the inside strap, in order to provide a calking 
edge on the outside with as little pitch or distance between the rivets 




Fig. 12. Double-Riveted Butt Joint 



as possible; the effectiveness of calking is dependent upon the ability 
of the rivets to hold the sheets in close contact. Obviously, the 




Fig. 13. Treble-Riveted Butt Joint 



farther apart the rivets are along the calking edge, the easier it is 
for the sheet edge to spring away from its companion sheet. 



24 CONSTRUCTION OF BOILERS 

TABLE IV 
Efficiencies of Double=Butt-Strap, Double=Riveted Joints 

Butt and Double-Strap Joints, Double Riveted, in Which the Pitch of Rivets in Outer 
Row Is Twice the Pitch of Rivets in the Second Row. 







A" Plate 
f" Butt Straps (or thicker) 
J" Rivet (before driving) 



Diameter 

of 

Rivet 

Hole 


DIMENSIONS 


LENGTH OF RIVETS 
BEFORE DRIVING 


J 


K 


L 


M 


Outer 
Row 


Second 
Row 


2 9// 
32 
15// 
16 


13// 
X 8 

17// 
ll6 


915// 

-^16 

3" 


5r 

5f" 


Hf" 


2|" 
2f 


2f" 
97// 

^8 



P 

Pitch of 

Rivets 

in Outer 

Row 




TENSILE STRENGTH 


OF PLATE 


(pounds) 


55000 


56000 | 


57000 58000 


DIAMETER OF RIVET HOLE 


ft' 


H\ 


§T 


W 


W 


w 


29 y 

32 


W 


4i " 


B79.8 


B79.1 


B79.8 


B79.1 


B79.8 


B79.1 


B79.8 


B79.1 


4&" 


B80.1 


B79.4 


B80.1 


B79.4 


B80.1 


B79.4 


B80.1 


B79.4 


4| " 


B80.4 


B79.7 


B80.4 


B79.7 


B80.4 


B79.7 


B80.4 


B79.7 


4H" 


B80.6 


B80.0 


B80.6 


B80.0 


B80.6 


B80.0 


B80.6 


B80.0 


4| " 


B80.9 


B80.2 


B80.9 


B80.2 


B80.9 


B80.2 


B80.9 


B80.2 


4H" 


B81.1 


B80.5 


B81.1 


B80.5 


B81.1 


B80.5 


B81.1 


B80.5 


4J " 


B81.4 


B80.7 


B81.4 


B80.7 


B81.4 


B80.7 


B81.4 


B80.7 


4&" 


B81.6 


B81.0 


B81.6 


B81.0 


B81.6 


B81.0 


B81.6 


B81.0 


5—" 


B81.8 


B81.2 


B81.8 


B81.2 


B81.8 


B81.2 


G80.7 


B81.2 


5&" 


B82.1 


B81.4 


B82.1 


B81.4 


G81.1 


B81.4 


G79.7 


B81.4 


5i - 


B82.3 


B81.7 


G81.5 


B81.7 


G80.1 


B81.7 


G78.7 


B81.7 


r_3_" 


G82.0 


B81.9 


G80.5 


B81.9 


G79.1 


B81.9 


G77.8 


G81.2 


5i " 


G81.0 


B82.1 


G79.6 


B82.1 


G78.2 


G81.6 


G76.+ 


G80.2 


K_5_" 


G80.1 


B82.3 


G78.6 


G82.1 


G77.3 


G80.7 


G75.+ 


G79.3 


5| " 


G79.1 


B82.5 


G77.7 


G81.1 


G76.4 


G79.7 


G75.+ 


G78.3 


K 7 // 


G78.2 


G81.7 


G76.8 


G80.2 


G75 + 


G78.8 


G74.+ 


G77 + 


51 " 


G77.3 


G80.7 


G76 + 


G79.3 


G74.+ 


G77.+ 


G73.+ 


G76 + 


K_9_" 


G76.5 


G79.8 


G75 + 


G78.4 


G73 + 


G77 + 


G72.+ 


G75 + 


5f " 


G75.6 


G78.9 


G74.+ 


G77.+ 


G73.+ 


G76.+ 


G71.+ 


G74 + 


eil» 


G74.+ 


G78 + 


G73.+ 


G76 + 


G72.+ 


G75 + 


G70.+ 


G74. 


5f " 


G73.+ 


G77.+ 


G72.+ 


G75.+ 


G71.+ 


G74 + 


G70.+ 


G73.+ 



The letters B or G show the manner in which the joint will fail. 
B = Strength of plate between rivet holes in outer row. 

G = Crushing strength of plate in front of two (2) rivets, plus the shearing strength of one 
(1) rivet in single shear. 

NOTE. — The highest efficiency in each column is shown in heavy figures. 



CONSTRUCTION OF BOILERS 25 

The criticism raised against lap joints as offering eccentric 
loads does not hold with double-butt-strap construction. 

Tables have been prepared for all types of riveted joints likely 
to be used, giving the efficiencies obtained by the use of different 
sheet thicknesses, different rivet sizes, and different rivet spacings. 
These include lap joints and butt joints; in the latter case, as com- 
plicated as quintuple riveting. In Table IV is given a sample data 
sheet of a double-butt-strapped, double-riveted seam for a A -inch 
plate. Note that several kinds of joint failures are worked out. 

CALKING 

In order that riveted joints of boilers may be steam and water 
tight, they require calking. This process upsets the metal of the 
overlapping plate, forcing it into close contact with the lower plate, 
and rendering the joint steam tight. 





Fig. 14. Correct Method of Calking Fig. 15. Incorrect Method 

of Calking 

Calking Tools. Hand Tools. The calking tool is similar to a 
chisel, the end having a variety of shapes. Fig. 14 shows a round- 
nosed tool which fullers the upper plate down without cutting the 
lower plate; but it is hard to start, and in calking with such a tool 
the edge is first started with a sharper round-nosed tool, and then 
finished with one as indicated in the figure. If a square-end tool is 
used, as shown in Fig. 15, the under plate is likely to be cut, and the 
plates between the edge and the rivet be separated. The most 
common form of calking tool is similar to the one shown in Fig. 14. 
Sometimes the end is flat, with a slight bevel, and not round. 

Pneumatic Calking Machine. A pneumatic calking machine is 
often used in boiler shops, as it does this work about four times as 
rapidly as it can be done by hand. The tool resembles a pneumatic 
hammer in appearance. Air is supplied through a flexible tube, at a 
pressure of about 70 pounds per square inch. 

Proper Method. A slight bevel given the plates makes calking 
more easily and securely done. "When the calking tool is thin it is 



26 



CONSTRUCTION OF BOILERS 



sometimes driven by careless workmen into the joint, wedging the 
plates open as shown in Fig. 15. Severe and careless calking is very 
injurious to boilers. On the inside it often causes grooving and 
fracture, and the fracture of plates then follows the line of calking 
rather than the line of rivet holes. 

WELDED JOINTS 

Advantages and Disadvantages. Welded joints for boiler work 
would be desirable if there were greater certainty in the results. By 
their use deposits which accumulate on and around rivet heads and 
joints, corrosion caused by leakage, and loose rivets and calking would 
be done away with. Moreover, a perfectly welded joint is stronger 
than the best riveted joint, and approximates nearly to the original 
strength of the plate. Welded steam drums are used for water- 




Fig. 16. Weld in Locomotive Fire Box 

Courtesy of C & C Electric and Man- 

ufacturing Company 



Fig. 17. Electrically Welded Boiler Flues 
Courtesy of Railway Master Mechanic 



tube boilers of the marine type and in the construction of cross pipes, 
mud drums, etc. Unfortunately it is impossible, from external 
appearances, to judge the soundness of a welded joint. The lack of 
tests on such joints and the small amount of information on the 
subject render the results of experiments of little value. The weld 
is best made when the edges of the plates are upset, at red heat, to 
nearly double the plate thickness, and beveled to an angle of about 
45 degrees. The edges are then heated together, and the weld made 
by hammering the joint down to the original thickness of the plate. 
Welding in boiler work finds its greatest usefulness in repair 
work, especially in such cases where any other method of repair 
would necessitate the removal of boiler sheets, or in places where 
any other work is difficult owing to lack of room. Boiler tubes are 



CONSTRUCTION OF BOILERS 



27 



sometimes welded to the tube sheets after the usual expanding is 
done. Figs. 16 and 17 are illustrations of cases in point. 

It is to be said in connection with welding of cracked boiler 
sheets, that there is danger that the sheet metal may have crystallized 
so much as to be unsuitable for good welding work. Many repair 
jobs are failures from this cause, which makes welding in boiler 
work less attractive than it otherwise would be. The welding of 
tubes into tube sheets of boilers makes it difficult to replace the 
tubes when they fail at a different place than the weld; it has been 
for this reason that w T elding for 
this purpose has made very little 
progress except in very special 
boiler designs. On the other 
hand, the welding of short pieces 
to the ends of tubes, after the 
ends have been cut off for re- 
moval from boilers, has long been 
successfully practiced. 

ARRANGEMENTS OF PLATES 
AND JOINTS 

Transverse and Longitude 
nal Seams. The tendency of a 
cylindrical shell carrying internal 
pressure to fail longitudinally 
is twice that circumferentially. 
Since this is the case, lap joints 
are used for transverse or girth 
seams, and stronger forms (butt joints) are used for the longitudinal 
seams. 

Complicated Joints. x\t the junction of three or more plates, 
where the circumferential and longitudinal joints meet, ordinary 
riveted joints would be too thick. To overcome this difficulty, two 
or more plates are forged thin at the joint, as shown in Fig. 18. 
The illustration shows a needless complication of joints at one place, 
but is given to emphasize scarfing as a means of obtaining strength. 

Whenever longitudinal and girth seams meet, the plates should 
be arranged to "break joints"; that is, one longitudinal seam should 




Fig. 18. Method of Handling Joint when 
Three or More Plates Meet 



28 



CONSTRUCTION OF BOILERS 



not be a continuation of another. The proper arrangement is shown 
in Fig. 19. 

In both vertical and horizontal boilers the inside lap is made 
to face downward, so that it will not form a ledge for the collection 
of sediment. 




Fig. 19. Part of Boiler Shell Showing Method of Breaking Joints 

Joints in Internally=Fired Boilers. The belts of plates which 
make up the length of the drums are sometimes arranged conically, 
with the outer sheet placed toward the direction of natural drainage. 
When the boiler is slightly inclined toward the front end, this conical 
arrangement facilitates draining and cleaning, as the dirt is removed 
at the front end. This is a great advantage in internally-fired 
boilers, as they are difficult to clean in any event. 

Joints in Vertical Boilers. In long vertical boilers the ring 
seams are arranged with the inside lap facing downward, so as not to 
have a ledge for sediment. Sometimes the belts of locomotive 
boilers are arranged telescopically, with the largest diameter at the 
fire-box end. Of late years the best makers use larger plates than 
formerly. This is advantageous, especially in externally-fired, multi- 
tubular boilers, as the single seam is placed above the water level, 
and therefore is away from the fire. 

Water=Leg Construction. The portion of internally-fired 
boilers between the shell and the furnace is called the water leg. 
Figs. 20 to 26, inclusive, illustrate the method of constructing the 



CONSTRUCTION OF BOILERS 



29 



water leg and the joints around the furnace doors. Figs. 20, 21, and 
22 show three methods of constructing the water leg. In Fig. 20 the 
exterior plate and the furnace plate are riveted to the ring D by 
means of long rivets. This ring is usually made of wrought iron, 
but in many cheap boilers it is of cast iron. In Fig. 21 the two plates 



B&Z W.: '#^^ 



fefc 



o 
o 

/o 
o 
o 
o 
o 

o 



o 

o 

6 E 

o 

o 

o 

o 

6* 



o 

o 
o 
o 
o 
o 
o 

o 



o o o o 






iiuHiHimiunm 



^ 



X7 



5 

o <f 

o 

o 
o 
o 
o 

%' 

o 
o 
o 
o 



% 



\\\\\\\\\\\\\\\\\\\ 



O 

o 

o 4 






) 



) 



Fig. 20. Form of Water-Leg Con- 
struction 




Fig. 21. Form of Water-Leg Con- 
struction 



are riveted to the flanged ring D. This construction is better than 
the solid cast-iron ring, on account of flexibility, but the junction of 
the plates D and C forms a corner in which sediment is deposited. 
In Fig. 22 the plate B is flanged and riveted to C. This arrange- 
ment requires less riveting than the one shown in Fig. 21. Figs. 
20, 21, and 22 also show three forms of construction of the joints 



30 



CONSTRUCTION OF BOILERS 



around the furnace door. In Fig. 20 
both the exterior plate and the furnace 
sheet are flanged and riveted together. 
This is shown in an enlarged view in Fig. 

23. The construction shown in Figs. 21, 

24, and 25 is not as good as that in Figs. 
20 and 23, because of the extra riveting; 
also, it has two corners, B and C, for the 
deposit of sediment. Fig. 22 shows a 
somewhat different form of furnace-door 
construction, the two plates being riveted 
to a cast-iron ring. This form is better 
shown in Fig. 26. It makes this part 
of the boiler too rigid, but it has the 
advantage of not having rivet heads in 
the door opening to wear off. In general, 
the flanged-ring method is preferable to 
the cast-iron ring, because of greater 
freedom for expansion, but the flanged 
ring forms undesirable corners for sedi- 
ment accumulation. 

Corner Joint Construction. In al- 
most every boiler, plates must be con- 
nected at right angles. An example of 
this is seen where the end plates are 

jointed to the shell plates of cylindrical boilers. There are three 

principal methods: riveting both plates to 

an angle iron, riveting both to a flanged 

ring, and flanging the end plate. In 

Fig. 27 the two plates are riveted to an 

angle iron, which is made of wrought or 

cast iron. This construction is too rigid; 

the constant variations of temperature 

cause repeated changes of form, which tend 

to crack the angle iron on the inside of the 

plate at the joint. Corrosion increases the 

evil, as it rapidly attacks iron which has 

« iiii r™ Fi »- 23 - Enlarged Section 

once been cracked or broken, ihere is no of Door joint, Fig. 20 




Fig. 22. Form of Water-Leg 
Construction 







fill 


p ilpi 





CONSTRUCTION OF BOILERS 



31 




Fig, 



. 24. Enlarged Section of Joint 
Construction in Fig. 21 




definite rule for the dimensions of these 
angle irons, but it is safe to make the 
mean thickness a little greater than that 
of the plates. 

The forms shown in Figs. 28 and 29 
are better. The head is flanged and riv- 
eted to the shell plates. The flanging 
makes a more flexible joint. The radius 
of the curve of the flange should be at 
least four times the thickness of the plate. 
The head and shell are sometimes con- 
nected to a flanged ring, as shown in Fig. 
30; the extra row of rivets makes a more 
complex joint, and the construction, since 
it need not be used, should be avoided. 

In vertical boilers the external fire 




Fig. 25. Enlarged Section of Joint 
Construction in Fig. 21 



Fig. 26. Enlarged Section of Joint 
Construction in Fig. 22 



box is joined to the cylindrical shell by riveted joints. Figs. 31 and 
32 show two forms, that in Fig. 31 being the better on account of 
the flanged ring, which allows expansion and contraction of the 
shell and furnace plates. 





Fig 27. Corner 

Joint with Angle 

Plate 



Fig. 28. Corner 

Joint with Flanged 

Head 



Fig. 29. Corner 

Joint with Flanged 

Head 



Fig. 30. Corner 

Joint with Flange 

Ring 



32 



CONSTRUCTION OF BOILERS 



Sometimes the case occurs of connecting two plates which are 
parallel and near together. At the bottom of the locomotive fire 
box a connection must be made between the inner and outer shells 
of the fire box. Several methods for this construction are shown in 





Fig. 31. External Fire-Box Con- 
nection with Flanged Ring 



Fig. 32 External Fire-Box Con- 
nection with Angle Plate 



Fig. 33. Fig. 33^4 is too complicated and is undesirable, both on 
account of the numerous rivets and angle irons, and on account of the 
inside joints, which cannot be calked. Fig. 335 is better, since it 
has but one angle iron; it has, however, the undesirable inside joint. 




Fig. 33. Different Forms of Locomotive Fire-Box Connections 

Fig. 33Z) is a good joint, the form of connecting ring being channel 
iron. Fig. 33E, as we have seen, is a good flexible joint, but it has 
the undesirable corner where sediment lodges. 

It is to be remembered that the use of structural steel in the 
construction of high-pressure boilers should be avoided, and to this 
extent the forms of water-leg construction illustrated cannot be 
universally used. 



CONSTRUCTION OF BOILERS 33 

MANHOLES 

Location. In order to provide access to the inside of boilers, 
manholes are constructed either in the flat end sheets of the shells 
or through the curved cylindrical sheet. These openings are, of 
course, located so that highly heated gases will not strike them, 
and they are made elliptical in shape, as this form offers the greatest 
opening for a given amount of material removed; it also lends itself 
best to the conservation of the strength of the removed boiler sec- 
tion, and, having one dimension greater than [the other, permits 
the insertion of a cover plate for the opening which will carry the 
internal pressure by being forced upon its seat. When located in 
the cylindrical surface, the longer dimension is in the direction of 
the girth seam, as the tendency to rupture in that direction is only 
half that of the longitudinal dimension of the shell. 

Size of Opening. Manhole openings should not be less than 
11 by 15 inches in size in the clear opening and, if strength permits, 
it is well to make them larger 
in both dimensions. In order to 
strengthen the opening, a man- 
hole frame or reinforcing ring is 
riveted around the openings, as 
shown in Fig. 34. 

Frame Construction. This 
frame or other reinforcing ring 
is made of wrought or cast steel 

having a net CrOSS-Sectioiial area, Fig- 34. Method of Riveting Manhole 

Frames to Shells or Drums with Two 

on a line parallel to the axis of Rows of Rivet5 

the shell, not less than the cross-sectional area of shell plate 

removed on the same line, and of no less thickness than the shell 

plate. 

Manhole frames on shells or drums must have proper curvature, 
and on boilers over 48 inches in diameter should be riveted to the 
shell or drum with two rows of rivets, which may be pitched as 
shown in Fig. 3-4. The strength of the rivets in shear on all manhole 
frames and reinforcing rings should not be less than the tensile 
strength of the shell plate removed, on a line parallel to the axis of 
the shell, through the center of the manhole. 

Manhole plates should be made of wrought or cast steel. 




34 CONSTRUCTION OF BOILERS 

Construction with Flanged Edges. Manholes are sometimes 
made by flanging the edge of the hole inwardly, thus forming out of 
the sheet itself a reinforcing ring of great rigidity. The flanged edge 
is faced off to offer a suitable seat for the manhole plate. When this 
form of construction is used, especially in high-pressure boiler con- 
struction, a reinforcing ring is sometimes shrunk around the flanged 
edge, and both are then faced off. This construction, when prop- 
erly done, is probably the best possible form to build. 

Handholes. Handholes are needed to give access to the inside 
of boilers for the removal of sediment, for washing, and, in the case 
of water-tube boilers, for the cleaning and replacing of tubes. The 
principles of construction are the same for handholes as for manholes, 
though the use of reinforcing rings is not resorted to because, being 
smaller, the strength of the sheet is not so seriously impaired as 
with manholes. They are always made elliptical in shape except in 
water-tube boilers, in which case they may be of round or of irregu- 
lar shape. The elliptical shape has the advantage of permitting 
the plate to be independently removable, at the same time carry- 
ing the pressure by forcing the handhole plate upon its seat. The 
flanging of the handhole openings in water-tube boilers is rapidly 
finding greater use on account of the greater stiffness of the plate 
around the hole and for the other advantages just mentioned. 

STAYS 

Necessity of Staying Flat Surfaces. When under steam, a 
cylindrical shell is under stress due to internal pressure in two direc- 
tions, namely, transversely, by a circumferential stress due to the 
pressure tending to burst the shell by enlarging its circumference, 
and, longitudinally, by the pressure on the ends. A spherical boiler 
would require no stays, because a sphere subjected to internal pres- 
sure tends to enlarge but not to change its shape. All flat surfaces 
in boilers must be stayed, otherwise the internal pressure would 
bulge them out and tend to make them spherical in shape. To 
avoid stays the ends of steam drums on high-pressure water-tube 
boilers are made hemispherical, or nearly so. 

The first and most important requirement in staying is to have 
a sufficient number of stays, so they will entirely support the plate 
without regard to its own stiffness. The second is to have them so 



CONSTRUCTION OF BOILERS 



35 



placed as to present the least obstruction to free inspection, and, 
third, to have them so arranged as to allow free circulation of 
water. Too much care cannot be taken in fitting stays and braces, 
as they are out of sight for long periods, and a knowledge of their 
exact condition is not always easy to be obtained. In fire-tube 
boilers the principal surfaces stayed are: the flat ends, crown sheets, 
water legs of locomotive boilers, and combustion chambers of cylin- 
drical marine boilers. In the 
case of most Scotch marine 
boilers, the diameter is large 
compared to the length; 
hence there is considerable 
flat surface. All the plates 
that are not cylindrical or 
hemispherical must be stayed. 
The details should be ar- 
ranged for each boiler; a few 
general methods and cautions 
may, however, be given. 

Simple Stay Rod. The most common and simple form of stay 
is a plain rod. It is used to stay the flat ends of short boilers. This 
stay is a plain rod passing through the steam space and having the 
ends fastened to the heads. The ends are fastened and the length 
adjusted by a variety of methods, the simplest being nuts on both 
sides of the plate, as shown in Fig. 35. The copper washers a and b 
strengthen the plate and prevent abrasion by the nuts. In place 
of the nuts the rod is often bolted to angle irons, which are riveted 
to the plates. In this case, turnbuckles similar to the one shown 
in Fig. 36 are used for adjusting the length. 




Fig. 35. Method of Fastening Stay Rods 




Fig. 36. Turnbuckle Used to Tighten Stay Rods 

The stays are made of wrought iron or steel, with an allowable 
stress of 5000 to 7000 pounds per square inch. If the ends are 
fastened to riveted angle irons, the combined area of the rivets is 
made a little greater than that of the rod. 



36 



CONSTRUCTION OF BOILERS 



Qusset Stay. If a boiler is long, say, more than 20 feet, through 
stays would sag in the middle and not take up the full stress on the 
end plates. For long boilers, gusset and diagonal stays are used. 
The form of boiler stay shown in Fig. 37 is made of wrought-iron 
plate riveted to angle irons, the angle irons being riveted to the end 
and shell. Boilers of the Cornish, Lancashire, and Galloway types 



fi>ttt/fotNtffriM/fouuft>,n &i. 




Fig. 37. Corner of Boiler with Gusset Stay 

often have this kind of stay. These boilers are internally fired and, 
as the variation of temperature causes expansion and contraction, 
great care should be used in placing the gusset stay. If the stay is 
too near the flange or if too many stays are used, the head will be 
too rigid and have a tendency to crack. 



r\ r\,r\,r\ 




Fig. 38. Diagonal Stay Using Angle Irons 
and Pins 



Diagonal Stays. A form of diagonal stay is shown in Fig. 38. 
The plain rod is connected to angle irons by means of pins. The 
angle irons are fastened to the shell and end by rivets or bolts. 
Another form of diagonal stay, called the crowfoot, is shown in Fig. 
39. The two ends are bolted or riveted to the end and shell. 



CONSTRUCTION OF BOILERS 



37 



The angle between the shell plate and stay rod should be small 
— not more than 30 degrees. The rod itself is designed for tensile 
strength, since the diagonal pull may be easily reduced to an equiva- 
lent direct pull. A large factor of safety is used to provide for 
future corrosion. 




Fig. 39. Form of Crowfoot Stay 

For marine boilers, a modified crowfoot stay, Fig. 40, is often 
used. The end passing through the head is supplied with nuts and 
taper washers, the washers having the proper taper to allow the 
nuts to be set up tightly against them. 

It should be added that boiler heads are further stiffened by 
channel bars or angles placed along the line of holes for the through 
stay rods. 

Riveted Stay Bolts. In loco- 
motive fire boxes and in the com- 
bustion chambers of marine boil- 
ers, there are two flat or slightly 
curved surfaces which must be 
stayed together. These are riv- 
eted by short screw stay bolts. 
The bolts shown in Figs. 41 and 
42 are screwed in place, and the 
ends riveted over. In marine 
boilers these stays are fastened 
with nuts, as shown in Fig. 43, instead of being riveted. Some- 
times the bolt is threaded the entire length, as in Fig. 41, or 
is turned off smooth in the center, as in Fig. 42. The smooth sur- 
face resists corrosion, and is less likely to fracture than the threaded 
bolt. Sometimes a small hole is drilled in the end, so that if the 




Fig. 40. Form of Fastener for Marine 
Type of Crowfoot Stay 



38 



CONSTRUCTION OF BOILERS 



bolt breaks, the escaping steam will give warning. This is shown 
at a Fig. 42. These bolts are £ inch or 1 inch in diameter. 

The stresses which come on a stay bolt are not the same as the 
stresses on rivets or on ordinary stay rods; as a matter of fact, stay 




Fig. 41. Riveted Locomotive 
Stay 



Drilled Form of Riveted 
Locomotive Stay 



bolts fail by a bending stress, and generally fracture just inside the 
outside sheet, due to the unequal expansion between combustion 
chamber, or furnace, and the outside boiler shell. Owing to this 
difference of expansion, flexible stay bolts have been designed, but 
have not come into general use; nor are they likely to, as they occupy 
considerable space and are much more complicated than the simple 
stay bolt. Stay bolts are made from the best quality of refined 
iron, w T hich has been found to stand the stresses of alternate heating 
and cooling better than mild steel. Iron stay bolts are more dura- 
ble, because of the fibrous nature of the iron. 

Stiffening Angles. Where 
the size of the boiler shell is 
not large and the pressure is not 
especially high, it is permissible 
to use stiffening angles in lieu of 
stays to prevent the end sheets 
of cylindrical shells from bulg- 
ing. The accompanying illus- 
tration, Fig. 44, shows the de- 
tails of such a construction and needs no further explanation. The 
illustration can be studied to advantage in other particulars as it 
gives the tube spacing, the size and location of a handhole, the 
proper levels of the gage cocks and the water, and the location of a 
fusible plug in the case of a 36-inch horizontal tubular boiler. 

Crown Sheet Supports. The crown sheets of fire boxes and 
tops of combustion chambers are usually stayed by crown bars, 
which extend across the flat surfaces, Fig. 45, the ends resting on the 




Fig. 43. Marine Stay Held with Nuts 



CONSTRUCTION OF BOILERS 



39 







Li 



Fig. 44. Method of Staving Boiler Heads with Steel Angles 




fl 



m 



Sec!>0"Flfl 



Fig. 45. Crown Sheet Support for Combustion Chamber in Scotch Marine Boiler 



40 



CONSTRUCTION OF BOILERS 



side plates. Bolts about 4 inches apart connect the crown sheet to 
this girder. The girder may be a solid bar, or it may be made 
up of two flat plates bolted or riveted together, as shown in the 
figure, the stay bolts being placed between the plates at intervals 
of about 4 inches. Either bolts or rivets may be used to keep the 
plates which form the girder from spreading. Projections are 
sometimes forged on the bottom of the girder, so that the stay bolts 
may be screwed up tightly without bending the plate. 

The depth of the plates which make up the girder varies from 
4 to 6 inches. They are from f to f inch in thickness. If bolts J 
inch in diameter are used, the distance between the plates is usually 
1 inch, but if bolts 1 inch in diameter are used, the distance should 




Fig. 46. Crown Sheet Support by Use of Sling Stays 



be 1| inches. The ends of the bars which rest upon the side plates 
should be carefully fitted to make a good bearing, and the area 
should be sufficient to prevent crushing of the end plates. The 
distance between the crown sheet and the girder should be at least 
1| inches, so there will be good circulation and the plates may be 
readily cleaned. 

In some cases the girder is supported from the shell by sling 
stays, as shown in Fig. 46. The sling stays are connected to the 
girder and to an angle iron, or T-iron, which is riveted to the shell. 
The angle iron stiffens the shell. In designing this form of stay 
it is usual to make the girder strong enough to support the crown 
sheet without any sling stays, and these stays are used for addi- 
tional support. 



CONSTRUCTION OF BOILERS 



41 



TABLE V 
Maximum Allowable Stress for Stays and Stay Bolts 



Material and Type 



Size up to and 
Including \\i 
In. Diameter 
or Equivalent 
Area, Lb. 



Size Over \\i 

In. Diameter 

or Equivalent 

Area, Lb. 



Weldless mild steel head to head or through 
stays 

Weldless mild steel diagonal or crowfoot stays 

Weldless wrought-iron head to head or through 
stays 

Weldless wrought-iron diagonal or crowfoot 
stays 

Welded mild steel or wrought-iron. stays. . . . 

Mild steel or wrought-iron stay bolts 



8000 
7500 

7000 

6500 
6000 
6500 



9000 
8000 

7500 

7000 
6000 
7000 



A horizontal tubular boiler, having a manhole below the tubes, 
should have one or more stays on each side of the manhole, the rear 
ends of which should be attached to the rear head of the boiler and 
the front ends allowed to pass through the front head secured with 
nuts, inside and out. The center line of such stays at the front head 
should not be below the center line of the manhole. 

Stay rods ought not to exceed 3 feet in length when screwed 
through the sheets and riveted over. 



TABLE VI 
Allowable Loads on Stay Bolts with V=Threads, 12 Threads per Inch 



Outside Diameter 

of 

Stay Bolts 

(In.) 


Diameter at 

Bottom of 

Thread 

(In.) 


Net Cross- 
Sectional 
Area (at 
Bottom of 
Thread) 
(Sq. In.) 


Allowable 
Load at 
6500 Lb. 

Stress, per 
Sq. In. 


Allowable 
Load at 
7000 Lb. 

Stress per 
Sq. In. 


3 

4 


0.7500 


0.6057 


0.288 


1872 


2016 


13 
16 


0.8125 


0.6682 


0.351 


2282 


2457 


7 
8 


0.8750 


0.7307 


0.419 


2724 


2933 


15 
16 


0.9375 


0.7932 


0.494 


3211 


3458 


1 


1.0000 


0.8557 


0.575 


3738 


4025 


1A 


1.0625 


0.9182 


0.662 


4303 


4634 


11 


1 . 1250 


0.9807 


0.755 


4908 


5285 


1A 


1.1875 


1.0432 


0.855 


5558 


5985 


n 


1.2500 


1 . 1057 


0.960 


6240 


6720 


i& 


1.3125 


1 . 1682 


1.072 


6968 


7504 


it 


1.3750 


1.2307 


1.190 


7735 


8330 


l* 


1.4375 


1.2932 


1.313 


8535 


9191 


li 


1.5000 


1.3557 


1.444 


9386 


10108 



42 



CONSTRUCTION OF BOILERS 



TABLE VII 
Allowable Loads on Stay Bolts with V -Threads, 10 Threads per Inch 



Outside Diameter 

of 

Stay Bolts 

(In.) 


Diameter at 

Bottom of 

Thread 

(In.) 


Net Cross- 
Sectional 
Area (at 
Bottom of 
Thread) 
(Sq. In.) 


Allowable 
Load at 
6500 Lb. 

Stress, per 
Sq. In. 


Allowable 
Load at 
7000 Lb. 

Stress per 
Sq. In. 


u 


1.2500 


1.0768 


0.911 


5921 


6377 


1A 


1.3125 


1 . 1393 


1.019 


6623 


7133 


H 


1.3750 


1.2018 


1.134 


7371 


7938 


i& 


1.4375 


1.2643 


1.255 


8157 


8785 


H 


1.5000 


1.3268 


1.382 


8983 


9674 


i 16 


1.5625 


1.3893 


1.515 


9847 


10605 


1^ 


1.6250 


1.4518 


1.655 


10757 


11585 



Load on Stay Bolts. Flat surfaces, other than segments of 
heads, must be stay-bolted, or stayed by welded or weldless mild 
steel or wrought-iron head to head or through, or diagonal or crow- 
foot stays. 

The maximum allowable stress per square inch net cross- 
sectional area of stays and stay bolts should be as given in Tables 
V, VI, and VII. 

Areas of Segments of Heads to be Stayed. The area of a seg- 
ment of a head to be stayed is the area enclosed by lines drawn 3 
inches from the shell and 2 inches from the tubes, as shown in Figs. 
47 and 48. 

When a flat head has a manhole opening, the flange of which 
is formed from the solid sheet and turned inward to a depth of not 
less than twice the thickness of the head, an area 2 inches wide all 
around the manhole opening, as shown in Fig. 49, may be deducted 
from the total area of head, including manhole opening, to be stayed. 



BOILER TUBES AND FLUES 

Spacing of Tubes. Just as the placing of rivet holes in the sheet 
of a shell boiler reduces the strength of the shell against longitudinal 
rupture, so does the drilling of holes for the insertion of tubes weaken 
the plate. In some forms of water-tube boilers the steam and water 
drums are connected by water tubes which enter the drums along 
longitudinal lines or parallel with the longitudinal seams. It is 
obvious that, should the result of such a construction show that the 






CONSTRUCTION OF BOILERS 



4? 




Fig. 47. Method of Determining Net Area of Segment of a Head 




Fig. 48. Method of Determining Net Area of Irregular Segment of a Head 




Fig. 49. Method of Determining Net Area of Segment of Head Containing 
Manhole Opening 



44 



CONSTRUCTION OF BOILERS 



shell is weaker along the tube line than along the longitudinal rivet 
seam, the efficiency of the sheet along the tubes should be used for 
determining the allowable pressure on the boiler rather than that of 
the riveted joint. The material remaining between two adjacent 

Longiludinol Line >■ 

Fig. 50. Diagram of Tube Spacing with Pitch of 
Holes Equal in Every Row 

tubes expanded into either the cylindrical or the flat part of a 
boiler construction is termed the ligament. 

Efficiency of Ligament The formulas which follow, as well as 
examples, are taken from the "Preliminary Report of the Committee 

~ai'4* *4"±s&£ ef'H*s4"4« a'-XtrX 

Longitudinal Line ■■ ■ > ■ 

Fig. 51. Diagram of Tube Spacing with Pitch of Holes 
Unequal in Every Second Row 

of The American Society of Mechanical Engineers to Formulate 
Standard Specifications for the Construction of Steam Boilers". 
When a shell or drum is drilled for tube holes in a line parallel to the 

SHS-e-e-®-®-® -&($-< 

k s4"± er'*\* 54"^ s4"± e4" ^ si'% e4"^ *>4 ,7 £ &'■ 
H z&4- 



L ongi ludinol L ine 




Fig. 52. Diagram of Tube Spacing with Pitch of Holes Varying Every Second 
and Third Row 

axis of the shell or drum, the efficiency of the ligament between the 
tube holes shall be determined as follows: 

1. When the pitch of the tube holes on every row is equal (Fig. 50), 
the formula is 

= efficiency of ligament 



CONSTRUCTION OF BOILERS 45 

in which p is pitch of tube holes in inches, and d is diameter of tube 
holes in inches. 

Example. Pitch of the tube holes in the drum of a water-tube boiler 
equals 5J inches or 5.25 inches. Diameter of tube holes equals 3J inches or 3.25 
inches. 

, = - ' w = 0.38 efficiency of ligament 

2. When the pitch of tube holes on anyone row is not uniform 
(Figs. 51 or 52), the formula is 

• — - — = efficiency of ligament 

in which P is unit length of ligament in inches; n is number of tube 
holes in length P; and d is diameter of tube holes in inches. 

Examples. 

1. — p — =s— — — — : — =0.458 efficiency of ligament 

P-nd 29.25-5X3.25 ft ' ' . fV 

2. — p — = oqo^ = 0-461 efficiency of ligament 

3. When a shell or drum is , , 

drilled for tube holes in a line diagonal -Z^PX-Zi^L J^!l\ _/^' N \ 

with the axis of the shell or drum, as \l/ \!/ ~VL/ V \~s 

in Fig. 53, the efficiency of the liga- 
ment between the tube holes shall be 
determined as follows: 

= efficiency of ligament 

in which P is diagonal pitch of tube 

holes in inches; d is diameter of tube Girth Line 

holes in inches; and v is distance be- Fi e- J>3. Diagram of Tube Spacing with 

. ' , . i. ii Tube Holes in Diagonal Lines 

tween rows of tubes, longitudinally. 

4. Diagonal pitch of tube holes in the drum of a water-tube boiler equals 
6.42 inches. Diameter of tube holes equals 4 inches. Distance between rows 
of tubes, longitudinally equals 5.75 inches. 

6 42— 4 

- L z-==— = 0.42 efficiency of ligament 

O. § D 

Spacing of Tubes in Flat Water Legs. The construction of 
stayed box-header water-tube boilers requires that considerable 
attention be paid to the tube spacing judged from the standpoint 
of obtaining strength in keeping with the remainder of the boiler. 
It will be recognized that, should the ligament rupture, the whole 
boiler head may have to be discarded, as repairs are very difficult 




46 



CONSTRUCTION OF BOILERS 

TABLE VIM 
Lap-Welded Boiler Tubes 



X rt c 

w5~ 


u 

©Co 


$ m 


© 

H-* © 

5 


© 
— a 
2 2* 

*> a © 

x § « 

3 


£ era 


c3 
© 
U 
< © tn 

— b ^ 

13-3 

5 era 

©CCHH 


el 

© W. 


© 
©-a 

■§J 

^2 

«♦* °^ 

o • © 

ir © 

■+^ _i 
be a 1 
c M 

© u 
»_} © 

Pi 


5 §-3 


1 


.856 


.072 


2.689 


3.142 


.575 


.785 


4.460 


3.819 


.708 


1J 


1.106 


.072 


3.474 


3.927 


.960 


1.227 


3.455 


3.056 


.900 


H 


1.334 


.083 


4.191 


4.712 


1.396 


1.767 


2.863 


2.547 


1.25 


if 


1.560 


.095 


4.901 


5.498 


1.911 


2.405 


2.448 


2.183 


1.665 


2 


1.804 


.098 


5.667 


6.283 


2.556 


3.142 


2.118 


1.909 


1.981 


21 


2.054 


.098 


6.484 


7.069 


3.314 


3.976 


1.850 


1.698 


2.238 


2| 


2.283 


.109 


7.172 


7.854 


4.094 


4.909 


1.673 


1.528 


2.755 


2f 


2.533 


.109 


7.957 


8.639 


5.039 


5.940 


1.508 


1.390 


3.045 


3 


2.783 


.109 


8.743 


9.425 


6.083 


7.069 


1.373 


1.273 


3.333 


3J 


3.012 


.119 


9.462 


10.210 


7.125 


8.296 


1.268 


1.175 


3.958 


3i 


3.262 


.119 


10.248 


10.995 


8.357 


9.621 


1.171 


1.091 


4.272 


3f 


3.512 


.119 


11.033 


11.781 


9.687 


11.045 


1.088 


1.018 


4.590 


4 


3.741 


.130 


11.753 


12.566 


10.992 


12.566 


1.023 


.955 


5.32 


4-i 


4.241 


.130 


13.323 


14.137 


14.126 


15.904 


.901 


.849 


6.01 


5 


4.720 


.140 


14.818 


15.708 


17.497 


19.635 


.809 


.764 


7.226 


6 


5.699 


.151 


17.904 


18.849 


25.509 


28.274 


.670 


.637 


9.346 


8 


7.636 


.182 


23.989 


25.132 


45.795 


50.265 


.500 


.478 


15.109 


10 


9.573 


.214 


30.074 


31.416 


71.975 


78.540 


.399 


.382 


22.190 


12 


11.542 


.229 


36.260 


37.699 


103.749 


113.097 


.330 


.318 


28.516 


16 


15.458 


.271 


48.562 


50.265 


187.667 


201.062 


.247 


.238 


45.200 


20 


19.360 


.320 


60.821 


62.832 


294.373 


314.159 


.197 


.190 


66.765 



to make between tubes expanded into a flat plate. The fact that 
stay bolts are a necessary part of this construction imposes greater 
difficulties than is the case of expanding tubes in the head of a hori- 
zontal tubular boiler. The best boiler makers resort to using tube 
sheets thicker than seem to be required by calculations of efficiency, 
thus using high factors of safety for this important part of the con- 
struction. 

Tube Holes and Ends. Tube holes are drilled full size, or they 
may be punched not to exceed \ inch less than full size, and then 
drilled, reamed, or finished full size with a rotating cutter. 

The edges of tube holes should be chamfered to a radius of 
about x§ inch. 

A fire-tube boiler has the ends of the tubes beaded, while water- 
tube boilers should have the ends of all tubes, suspension tubes, and 
nipples flared not less than \ inch over the diameter of the tube 
hole. 



CONSTRUCTION OF BOILERS 47 

The ends of all tubes, suspension tubes, and nipples of water- 
tube boilers must not project through the tube sheets or headers 
less than J inch nor more than | inch. 

When it is necessary to place a fusible plug in a tube, an extra 
thick tube must be provided for that purpose. 

Types of Tubes. Boiler tubes are given the names they would 
naturally have, so as to be most descriptive, the most usual grades 
being lap-welded steel, charcoal-iron, hot-roiled seamless steel, and 
cold-drawn seamless steel. The most commonly used tubes are 
lap welded because they are the cheapest. All grades are manu- 
factured in the gages most usually demanded; the outside diameter 
of the tube is used to designate its size. 

Lap-welded tubes are formed from a flat plate, the edges of 
which are upset, then bent around until the thickened edges lap 
sufficiently. It is then heated successively about 8 inches at a time 




Fig. 54. Type of Prosser Expander 
Courtesy of Joseph T. Ryerson and Son, Chicago 

and w r elded over a mandrel, which is a cast-iron arm with a slightly 
convex top, over which the tube is placed. Table VIII gives the 
dimensions of standard lap- welded tubes. 

Methods of Expanding Tubes. Tubes are fastened to the tube 
sheets by expanding the metal of the tube into the tube hole. This 
is done by a tool called an expander, of which there are two common 
forms. 

Prosser Expander. The Prosser expander consists of a steel 
taper pin and a number of steel segments, held in place by a spring. 
The outside of the segments have the form to be given to the 
expanded tube, and the inside is a straight hollow cone, into which 
the steel taper pin fits, Fig. 54. The segments are forced apart by 
hammering on the steel pin. In order that the metal of the tube 
may not be injured, the hammering should be done gradually and 
carefully, and the expander turned frequently. 



48 



CONSTRUCTION OF BOILERS 



Dudgeon Expander. The Dudgeon expander, Fig. 55, has a set 
of rolls that are forced against the inside of the tube by turning the 



WKKH'^^m fpi* If 



Fig. 55. Type of Dudgeon Expander 
Courtesy of Joseph T. Ryerson and Son, Chicago 

taper pin. The pin and rolls rotate as the pin is driven, and the 
rolls gradually expand the tube against the tube plate. 

Fig. 56 shows the effect of using a Prosser type of expander 
though the distortion of the tube is greatly exaggerated. Fig. 57 
shows the effect of using a Dudgeon type of expander. 

After the tubes are expanded, the ends are beaded over as 
shown in Figs. 56 and 57. This adds to the strength of the con- 
nection between the tube and tube sheet. Beading over is not 
usually resorted to when expanding water tubes. 

Stay Tubes. Stay tubes are not used as extensively at the 
present time as they were formerly. They were very common at a 
time when the holding power of expanded tubes had been experi- 




Fig. 56. Section of Prosser Expansion 
with Distortion Exaggerated 



Fig. 57. Dudgeon Expansion 



mented on but little. It is now apparent from such tests that the 
holding power of tubes expanded, as shown in Fig. 56, is more than 



CONSTRUCTION OF BOILERS 



49 



equal to the pressure on the spaces between the tubes of an ordinary 
tube plate. Stay tubes are simply heavier tubes, with the ends pro- 




Fig. 58. Stay-Tube Details 



jecting beyond the tube sheet and threaded for shallow nuts. The 
ends of the tubes are frequently upset or thickened, and screwed 
into the tube sheet as well. Both forms are shown in Fig. 58. 




Jr 



fifei 






Fig. 59. Adamson Ring Furnace 



Fig. 60. Furnace Construction Not as 
Good as Fig. 59 



Furnace Flues. Flues which are subjected to external pressure 
are always cylindrical. Fig. 59 shows a section of the Adamson 




Fig. 61. Furnace Construction Not as Good as Fig. 59 

flue. This was an improvement over the plain furnace, as it is 
more elastic and allows expansion; the flanged rings also strengthen 



50 



CONSTRUCTION OF BOILERS 



and stiffen it against collapse. The methods of building furnaces 
shown in Figs. 60 and 61 are not considered as good as the Adamson 
arrangement. The method shown in Fig. 60 is too rigid, and does 
not allow expansion, while that of Fig. 61, on the other hand, is 
elastic; both have the fault of exposing a double thickness of plate 
and two rows of rivets to the fire at each joint. The ring sections 
are usually 18 inches in length. 

The Morison corrugated flue shown in Fig. 62 is popular and, 
furthermore, is excellent. There is freedom for expansion through- 



MMilM'M 



Fig. 62. Morison Boiler Flue 
Courtesy of Joseph T. Ryerson and Son, Chicago 

out its whole length, thereby reducing the stresses on the boiler. 
The plates should be thick enough to prevent sagging, the thick- 
ness usually varying from A to f inch. Corrugated furnaces are 
riveted to the rear tube sheet in a return-tubular boiler of the marine 
type, the end of the furnace being flanged at the front; the head of 
the boiler is flanged around the opening cut for the furnace, which 
fits well into the flange. 



BOILER REQUIREMENTS 

FACTORS IN DESIGNING BOILERS 

General Statement. In designing a steam boiler there are many 
considerations that must be kept in mind. Among the most impor- 
tant are strength, durability, capacity to furnish the required amount 
of steam, convenience for cleaning, repairing, and inspection, sim- 
plicity in detail, and economy both of running and first cost. 

The kind, or type, to be used depends upon the work to be 
done, the locality, and the available space and preference of the 
owner. The work to be done is determined by the number and 
kind of engines, the constancy with which they run, and the pres- 
sure. In choosing a boiler for any locality, the purity of the water, 



CONSTRUCTION OF BOILERS 51 

the kind of fuel, and the laws which govern inspection and allowable 
working pressure must be considered. The available space greatly 
influences the type and sometimes prevents a desirable choice in 
other particulars. For instance, locomotive and marine boilers 
must be adapted to small spaces. For stationary boilers, if the 
floor area is limited, but there is ample height, some type of vertical 
boiler may be chosen. 

Boiler Horsepower. The term "boiler horsepower" is mislead- 
ing, in that a boiler does not develop power but simply acts as a 
means for absorbing heat energy in one place and transferring it to 
a storage medium — the water and steam supplied to the boiler. 
The power element, when it appears, is found in the power produc- 
tion of the engines in which the steam is used. However, the mean- 
ing of the term has become so well understood by frequent use that 
no special confusion arises. The unit known as one boiler horse- 
power is the equivalent of the evaporation of 34.5 pounds of w r ater 
from and at 212 degrees F. Since each pound of water evaporated 
under the conditions given above represents the absorption of 970.4 
British thermal units, one boiler horsepower is equal to the absorp- 
tion of 33,479 B. t. u. By one boiler horsepower hour is meant the 
equivalent performance of a boiler horsepower during a period of 
an hour. This explanation is given so that the difference between 
engine horsepower and boiler horsepower will be borne in mind, as 
they are not of equal magnitude, nor of precisely the same physical 
significance. 

General Requirements. A boiler should have: 

1. Sufficient area of grate to burn the required amount of 
fuel. 

2. Enough heating surface to absorb the heat of combustion 
economically. 

3. Combustion chamber and flue area large enough to com- 
pletely burn and carry off the products of combustion. 

4. Water space sufficiently large so that a sudden demand will 
not cause too great a variation in water level. 

5. Surface of water large compared to volume, in order that 
steam may be readily disengaged. 

6. Steam space large enough to supply an irregular demand 
without causing a great change of pressure. 

7. Steam outlet large enough to supply steam to the engine 
without wiredrawing. 



52 CONSTRUCTION OF BOILERS 

If the outlet is not sufficiently large to supply plenty of steam, 
the demand will be greater than the supply and the steam will be 
throttled or wiredrawn, that is, it will lose some pressure. 

For all common types of boilers, the proportions between the 
above requisites have been determined by experiment. 

Area of Grate. Grates of the same area will burn different 
quantities of fuel in a given time, depending on the intensity of 
the draft, the character of the fuel and the fuel bed, and the kind 
of grate. For hand-fired grates the extreme length is usually from 
6 to 7 feet, the width being determined by the width of the furnace 
flue or boiler setting. For stoker-fired boilers the rate per square 
foot at which the fuel will burn in a unit time may be very much 
higher than for hand-fired grates with the same draft. If the 
mechanical stoker is of a type that removes the refuse accumula- 
tion as rapidly as formed, thereby keeping the fuel bed in an open 
condition, impediments to air flow through the bed are reduced 
to a minimum and the rate at which the fuel will burn rises. 
The main factor in determining the rate of combustion for a given 
furnace construction is the quantity of air forced through the fuel 
bed. Consequently, since in some types of boilers the grates are 
restricted in size owing to factors not capable of change, as, for 
instance, in locomotives, recourse is taken to artificial means for 
creating an intensity of draft much higher than would be obtained 
by the use of a chimney. 

It has been established as a fundamental truth that boilers 
absorb practically the same percentage of heat of the amount 
presented to them without regard to the actual quantity, other 
factors, such as pressure, remaining the same. Therefore, the way 
in which the fuel is burned has a great deal more to do with the 
over-all economy of the boiler unit with its grate and furnace than 
the boiler or heat absorber itself. Also, it is possible to burn the 
fuel at so low a rate that the combustion process is inefficient, 
although the degree of combustion may be practically complete. 
The area of the grate for a given boiler performance determines 
then the economy of performance. If too large, certain losses are 
inevitable for a given draft, and if too small, other losses may 
occur or the boiler may not deliver enough steam. Out of these 
facts the following conclusions may be arrived at: If, having 



CONSTRUCTION OF BOILERS 53 

selected a certain grate area, it is found that the operating per- 
formance is uneconomical, the grate area should be changed, 
making it either smaller or larger, depending on the steam require- 
ments and draft facilities. It is true that such an expedient is 
rarely adopted, because, in most instances, there is more than one 
unit and facilities are offered for operating the units in service 
according to fair standards by increasing or decreasing the number. 
A certain degree of elasticity is afforded by the use of boiler 
dampers which make it possible to change one of the main factors 
entering into the rate of combustion, namely, draft. 

Where mechanical stokers are employed, it is usually best to 
follow the suggestions of the manufacturers as to sizes, though in 
such instances they must be apprized of the available draft, furnace 
construction, and other factors, in order to give intelligent opinions. 

Water Evaporation per Pound of Fuel. The number of pounds 
of water a pound of fuel will evaporate depends upon the heat 
value of the fuel, the inherent ability of the boiler to absorb heat, 
the efficiency of the boiler furnace, the cleanliness of the heating 
surface, and the pressure of operation. It can easily be seen that 
so many factors, each independent of the others, may, when con- 
sidered together, result in incorrect conclusions. For purposes of 
comparison between different installations the actual evaporation is 
converted into terms of equivalent evaporation for feed water 
at 212° F. into steam at atmospheric pressure. When a boiler 
is selected the usual practice is to find out what the results are 
with fuel of a given character, judging from the results actually 
obtained in several installations; by the application of good judg- 
ment, it is possible to so proportion the grates and the draft 
facilities that equal or better results are obtained. 

The amount of water evaporated per pound of fuel is influ- 
enced by the character of the boiler construction, as, for instance, 
a boiler with good circulation, with its heating surface effective, is 
sure to give a better evaporative result than one not so well 
designed. The manner in which the boiler is inclosed, that is, the 
tightness of the setting, plays a very important part in the boiler 
performance. 

Boiler Rating. The horsepower at which boilers are rated may 
or may not have any relation to the actual boiler horsepower 



54 CONSTRUCTION OF BOILERS 

produced. The horsepower output of a boiler is dependent upon the 
amount of fuel burned and the efficiency of the boiler and furnace 
combined. It is quite desirable to rate boilers prior to their actual 
installation, and engineer's have come to establish arbitrary quan- 
tities of heating surface as the basis for rating boilers. The areas 
so selected have varied from time to time until at present it is 
generally accepted that 10 square feet of heating surface shall be 
considered one boiler horsepower rating in stationary practice. 

Steam Space. It is beginning to be realized that boiler space 
devoted to steam plays less of a factor in the successful operation 
of a boiler than was believed to be the case years ago. If the 
designs are fairly simple, such as in the cylindrical boiler, then 
the computations which are made regarding steam space are just 
as valid as ever; but for complicated designs, as in water-tube 
boilers, the steam space requirements do not apply as rigidly as 
for boilers with large bodies of water. In these instances it seems 
more important to pay strict attention to the places where violent 
ebullition takes place, as, for instance, at the front throat of a 
horizontal water-tube boiler, than to the actual space devoted to 
steam. Also the surface from which steam may be liberated plays 
a larger part in these boiler types than the actual water content. 
No set rules can be laid down for the complicated designs, but, 
for cylindrical boilers, an illustration of how to compute steam 
space will familiarize the student with a number of the problems 
involved in the subject. 

The steam space is frequently designed as some fraction of the 
interior volume of the boiler, usually about f . A better way is to 
design it from the steam consumption of the engine. Suppose the 
engine uses 30 pounds of steam at 75 pounds pressure per horse- 
power per hour. The absolute pressure then is 90 pounds (nearly) 
and the specific volume at that pressure is 4.85 (from steam 
tables). As steam is being generated at an approximately constant 
rate, the supply kept on hand need not be great. If the surface 
for the disengagement of steam is sufficient, the ratio of the steam 
space to the volume of the cylinder is from 50 : 1 to 150 : 1, 
depending upon the speed of the engine. Experiment shows that 
if the steam space is equal to the volume of steam consumed by 
the engine in 20 seconds, it is sufficient. If the space is equal only 






CONSTRUCTION OF BOILERS 55 



to the steam used in 12 seconds, a considerable quantity of water 
may be carried over with the steam. If the engine is slow speed, 
that is, less than 60 revolutions per minute, the steam space should 
be larger. 

The volume of the steam space per horsepower will be the 
number of pounds of steam used per horsepower in 20 seconds, 
multiplied by its specific volume, or 

30X4.85X20 Q1 u r ^ ^ u 

— 6Qx60 — = .81 cu. ft. (nearly) per h.p. 

If the engine is of 75 horsepower, the steam space will be 

.81X75 = 60.75 cu. ft. 

Heating Surface. The portion of a boiler that is exposed to 
the flames and hot gases is called the heating surface. This is 
made up of the portions of the shell below the brickwork, the 
exposed ends, and the internal surface of the tubes in fire-tube 
boilers. If the boiler is of the water-tube type, the exterior surface 
of the tubes is taken in place of the interior surface. 

The ability of heating surface to transmit heat to water 
depends upon cleanliness, circulation, and temperature of the gases. 
In designing it is safe to follow proportions of heating surface 
to grate area in the various types which experience has shown to 
give the best results. Hand-fired grates, for stationary practice, 
vary from 45 to 60 square feet of heating surface for each square 
foot of grate. In other types of boilers, such as locomotives and 
those using artificial draft, the proportions vary a great deal from 
these figures. If the boiler is of a type requiring baffles to cause 
the gases to impinge upon the heating surface, as in water-tube 
boilers, the effectiveness of the surface may be very much impaired 
by the construction. 

It is evident that some portions of the heating surface of a 
boiler are more useful than others. For instance, more heat will 
pass through the crown sheet, as it is in direct line of radiant 
heat, than through the last few feet of the tubes. 

If a cylindrical multitubular boiler is considered divided into 
equal sections, the section nearest the fire will evaporate more 
water than the one at the other end, as the gases have a higher 
temperature at the first section. Suppose the boiler be divided 



56 



CONSTRUCTION OF BOILERS 



into six sections of equal length, and call the total evaporation 100 
per cent. Then the per cent of evaporation per section will be 
approximately as follows: 



Section 


1 


2 


3 


4 


5 


6 


Evaporation 


47 


23 


14 


8 


5 


3 



If the length of a boiler is increased another section, the evapo- 
ration will be increased a little, but the radiating surface is 
increased at the same time. In case the addition of a section for 
evaporation causes a loss by radiation nearly equal to the gain in 
evaporation, it is not economical to add the section on account of 
the extra cost of the boiler. If forced draft is used, the boiler may 
be made longer without danger of impairing the draft. 

Allowable Pressure. According to Pascal's Law, liquids and 
gases exert pressure equally in all directions. Steam in a boiler 
exerts the same pressure on all portions of the shell. As the pres- 
sure inside a boiler is considerably greater than the pressure out- 
side (the atmospheric pressure), there is a tendency to burst the 
shell. This tendency is resisted by the plates of the boiler. 

A sphere is the strongest form to resist pressure, for since 
pressure is equal in all directions, there is a tendency toward 
enlarging the sphere and not to rupture. But because a sphere 
has the smallest area for a given volume and a large heating sur- 
face is desirable, and also on account of mechanical difficulties, a 
spherical boiler is never used. The boiler is made cylindrical to 
obtain greater heating surface, and the loss in strength is made up 
by staying. 

In considering the strength of cylinders, it is usual to divide 
the rupturing stresses into two classes: those which tend to rup- 
ture the cylinder longitudinally, and those which tend to rupture 
it circumferentially or transversely. The maximum pressure to be 
allowed on a steel or wrought-iron shell or drum of a boiler shall 
be determined from: the minimum thickness of the shell plates; 
the lowest tensile strength stamped on the plates by the plate 
manufacturer; the efficiency of the longitudinal joint or ligament 
between the tube holes, whichever is the least; the inside diameter 
of the outside course; and a factor of safety of not less than 5. 



CONSTRUCTION OF BOILERS 57 

T SxtX% 
The formula is — - — =^^ = maximum allowable working pressure 

in pounds per square inch, in which TS is tensile strength of shell 
plates in pounds; t is minimum thickness of shell plates in inches; 
% is efficiency of longitudinal joint or ligament between tube 
holes, whichever is the least; R is radius and is one-half the inside 
diameter of the outside course of the shell or drum ; and F S is the 
lowest factor of safety allowed on boilers in the district or munici- 
pality regulating the pressure allowed. 

Water-tube boilers are designed to make possible the use of 
smaller cylindrical shells, the drums being used merely to afford 
water and steam space through which the boiler proper, namely, 
the water, tubes, conveys the absorbed heat to the boiler outlet. 
Consequently, for the same thickness of sheets and rivet construc- 
tion, water-Jjibe boilers can operate at higher pressures than large 
shell cylindrical boilers, this constituting one of the particular 
advantages of the type. 

Sections. Boiler shells are made up in rings or sections. The 
length of the sections is often made equal, for convenience in 
ordering and cutting the plates. The length is limited by the 
width of plate obtainable and the size of the riveting machine. 
Shells 16 feet long would probably be made in three sections, but 
the lengths should be so adjusted as not to bring the ring seam 
over the hottest part of the fire. 

Furnace Flues. The internal pressure at which the boiler shell 
will rupture can be calculated, but the external pressure which will 
collapse a flue can be determined only by experiment or expe- 
rience. External pressure tends to increase any imperfection of 
shape. For instance, if a flue is slightly oval, external pressure tends 
to make it more flat; the strongest form to resist external pressure 
is evidently the circle. When considering the strength of flues, length 
is very important. If a lap joint is used the flue will not be a 
true cylinder; for this reason welded or butt joints are preferable. 

Attention is again called to the use of the Adamson furnace, 
Fig. 59, and the corrugated furnace, Fig. 62, as means of overcoming 
the tendency of furnace flues to collapse under pressure. 

Boiler Inspection During Manufacture. When purchasing a 
boiler, the character of workmanship employed by the manufac- 



58 CONSTRUCTION OF BOILERS 

turer should be carefully considered. If a factory employs more 
than one standard of workmanship, then it is highly important, 
if the best work is desired, to have facilities for knowing that the 
best standard of the factory is employed on the boilers ordered. 
All manufacturers can employ the best kind of workmanship, 
assuming they have the necessary equipment for bending sheets, 
beveling edges of sheets, power riveting, and flanging. 

The only way to be sure that a boiler is receiving the best 
workmanship is to engage someone to inspect the work as the 
parts are fabricated. The insurance companies have such inspectors, 
but they make a practice of inspecting the sheets for defects 
and rarely are present when the rivet holes are made, the sheets 
are bent, and the riveting performed. The advantage of having 
a boiler manufactured in a shop of only one standard, and that 
the best, is manifest. It is difficult to judge the workmanship of a 
boiler when once made. If then, as is true, the lives of many 
people may be jeopardized by poor workmanship in a high- 
pressure boiler, no effort should be spared to safeguard against a 
needless hazard, even though considerable additional expense has 
to be met in order to do so. 

The inspection and testing of sheets as stipulated by the engi- 
neering societies are extremely important and the data coming 
from these tests should be carefully inspected by competent 
persons. Wherever possible, after a boiler is fabricated, it should 
be tested in the shop. It frequently happens that certain parts of 
a boiler may be so tested without assembling. After the boiler 
has been erected in the field, without its setting or covering, a 
pressure test should be applied. It is customary to apply 50 
per cent more pressure than that allowed by the boiler construc- 
tion and laws. The water should be in the vicinity of 60° to 
70° F., and all leaks or "weepings" should be carefully noted, 
the pressure taken off, and the necessary calking performed. 
The pressure should then be applied again and repeated until no 
leakages occur. If the work has been properly done, usually 
very few leaks appear at the first application of pressure. 




o 

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03 «° 

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PART II 

TYPES OF BOILERS 



INTRODUCTION 

Function of a Simple Boiler. A steam boiler is a closed 
metallic vessel in which steam is generated from water by the 
application of heat. Only that part of a complete contrivance 
used for generating steam from water which is employed in the 
absorption of heat is known as the boiler. All of that portion of 
the arrangement in which the fuel releases its heat by fire is 
known as the furnace. Hence, the functions of the furnace and 
the boiler are exactly opposite; the former generating or liberat- 
ing heat, and the latter absorbing a part of this heat from the 
furnace. 

The purpose of a steam-generating equipment is to convert 
the available energy of fuel into heat energy carried by steam, so 
that it may be employed elsewhere, either in an engine in the crea- 
tion of mechanical energy or used, without conversion, as heat. 
Where the heat energy of the steam is to be converted into mechan- 
ical energy it is necessary to generate the steam at a greater pres- 
sure than that of the atmosphere. It follows that the boiler must 
be made amply strong to withstand the pressure intended, and 
must also be protected against the consequences of careless, unskill- 
ful, and dangerous operating methods. 

Boiler Accessories. To operate a boiler safely and econom- 
ically there must be certain fittings and accessories, some of which 
are used in the care of the boiler, while others serve to increase 
its economy. Among the most important of these are the fol- 
lowing: 

Feed Pump, or Injector. A feed pump, or injector, with valves, 
piping, etc., supplies water to the boiler. 

Gage Cocks and Water Gage. Gage cocks and glass water gage 
show the attendant the height of water, or the water level as it is 
called, in the boiler. 



2 TYPES OF BOILERS 

Pressure Gage. A pressure gage indicates the pressure of steam 
in the boiler. The pressure is usually measured in pounds per 
square inch. 

Safety Valve. A safety valve allows steam to escape from the 
boiler when the pressure exceeds a certain fixed amount. This attach- 
ment, being a safety device, should be automatic and reliable. 

Blow-Off Pipe. A blow-off pipe, with its valves, is used to blow 
out sediment from the boiler, reduce the amount of water in the 
boiler, or empty it. 

Steam Pipe. A steam pipe, with its valves, conducts the 
steam from the boiler to the place where it is to be used. 

Manholes and Handholes. Manholes and handholes, with covers, 
are used for making examinations, and when repairing or cleaning. 

Fusible Plugs* Fusible plugs are designed to give warning 
when the water level becomes too low. 

High- and Low-Water Alarms* High- and low-water alarms 
give warning when the water level is too high or too low. 

Heaters* A heater is a device for raising the temperature of 
the feed water to a point as nearly equal as possible to that of the 
water in the boiler. 

Columns, Lugs, or Brackets. Columns, lugs, or brackets are sup- 
ports for the boiler. 

Masonry. Masonry is used for enclosing the boiler and keeping 
it in position, and in many cases for keeping the hot gases in contact 
with the heating surface. 

Furnace Fittings. Furnace fittings include grate bars, bearer 
bars, fire doors, ash-pit doors, dead-plates, door-liners, etc. 

Damper Frame and Damper. The damper frame and damper 
are used to control the draft by varying the size of the opening 
through which the gases are allowed to escape from the boiler setting. 

Breeching. The breeching carries the gases from the boiler or 
its setting to the chimney. 

Chimneys. The chimney carries away the waste gases and 
creates draft. 

Tools. Tools include shovels, slice bars, scrapers, tube brushes, 
soot blowers, gasket mold s, etc. 

♦Although desirable, they are not absolutely necessary, as a boiler can be successfully 
operated without them. 



TYPES OF BOILERS 3 

CLASSIFICATION 

Basis of Classification. The almost endless variety of boilers 
now in use is due largely to the many conditions under which they 
are used. iVnother reason for the numerous forms is the resource- 
fulness of designing engineers, who, during the last century, have 
sought to produce, at moderate cost, steam generators which are 
at once safe, durable, and economical. 

A proper grasp of the subject requires that an orderly classi- 
fication of boilers be attempted. A number of different methods 
are employed for this purpose, but only those most commonly used 
are here given. Fortunately, many of the names applied to boilers 
are sufficiently descriptive, so that little difficulty will be found in 
locating a boiler in its particular field when once its proper name is 
known. Much valuable time may be saved, and a better under- 
standing of the subject gained, by selecting one design of boiler to 
represent a given class. Again, a classification tends to bring out 
interesting and important features. 

All boilers possess one or the other of the following pairs of 

characteristics : 

Fire Tube and Water Tube 

Vertical and Horizontal 

Stationary and Non-Stationary or Portable 

Externally Fired and Internally Fired 

There are some designs which employ both characteristics of 
a pair; for instance, a boiler .may have both fire tubes and water 
tubes; may not be distinctly either vertical or horizontal, but have 
a position midway between these two. 

Boilers are also classified according to the pressure at which 
they operate, and are then known either as high-pressure or low- 
pressure boilers. The pressure at which a boiler is intended to oper- 
ate determines only how strong the parts must be, and need not 
affect the selection of the scheme of putting the parts together. 
Consequently, low-pressure boilers and high-pressure boilers may be 
exactly alike in external appearance though their construction 
details and the materials of which they are made may be radically 
different. Besides, boilers designed to be used at high pressure are 
frequently used at low pressure. In view of the foregoing, a classi- 
fication based on pressures alone would not be especially service- 
able, even though to boiler manufacturers and engineers the expres- 



TYPES OF BOILERS 



sions "high-pressure" and "low-pressure" at once bring to mind 
characteristics of construction peculiar to each group. 

Scheme of Classification. The scheme of classification accord- 
ing to use and form is given as follows : 

Early Forms 

Plain Cylindrical 

Single Flue, Externally-Fired 



m 



g 

o 



Stationary 



Locomotive 



Marine 



( Cornish (Single-Flue) 
l 



Flue Boilers j Lancashire (Two-Flue) 
( Galloway 

Multitubular { g£^S& (Return-Tubular) 
Fire-Box Boilers horizontal 



Water-Tube Boilers 



Mixed Types 
Peculiar Forms 



Straight-Tube 

Curved-Tube 

Horizontal 

Vertical 

Sectional 

Non-Sectional 



Multitubular Fire-Box (Common Form) 
Wootten Type 
Corrugated Furnace 
Peculiar Forms 

Early Forms (Box or Rectangular) 
Scotch or Drum 
Return-Tubular 
Through-Tube 

f Curved-Tube 

Straight-Tube 

Sectional 

Non-Sectional 



Water-Tube 



Launch Boilers 



o 






Early Forms 



Flue 



Fire-Tube 
(Multitubular) 



Water-Tube 



Mixed Types 



Cornish (Single-Flue) 

Lancashire (Two-Flue) 

Galloway 

Single Flue (Externally-Fired) 

Horizontal (Common Form) 

Vertical 

Return-Tubular 

Through-Tube 

Fire-Box 

Peculiar Forms 



Horizontal 
Vertical 



Peculiar Forms 



Straight-Tube ( 
Curved-Tube l 
Straight-Tube 
Curved-Tube 



Sectional 
Non-Sectional 



TYPES OF BOILERS 5 

Definitions. The following definitions should be remembered: 

Fire- Tube Boiler. A fire-tube boiler is one having the heating 
surface composed largely of tubes which are surrounded by water, 
the hot gases passing through them. 

Water- Tube Boiler. A water-tube boiler is also composed of 
tubes, but in this case the water flows through the tubes, while the 
hot gases pass around them. 

Sectional Boiler. In a sectional boiler the tubes and corre- 
sponding headers form comparatively small units. Each unit is 
complete in itself; that is, it is in communication with a steam and 
water drum but is independent of the other units. 

Non-Sectional Boiler. A non-sectional boiler is one having all 
the tubes in communication with one another; in other words, all 
or nearly all the tubes are expanded into a common header or drum. 
The boiler is not made up of units. 

Single-Tube Boiler. A single-tube boiler is one which is made 
up of single tubes. 

Double-Tube Boiler. A double-tube boiler has a small tube 
inside of the regular tube and concentric with it. 

Externally-Fired Boiler. A boiler is externally fired when the 
furnace walls do not form a part of the boiler-heating surface but 
are built out of fire brick or other refractory material. 

Internally-Fired Boiler. In the internally-fired boiler the 
furnace walls are a part of the boiler-heating surface as well as a 
part of the furnace; the Scotch marine is a good example. 

Fire-Box Boiler. A fire-box boiler is one type of internally- 
fired boilers in which the furnace walls are flat or nearly so. The 
locomotive boiler is the best example. 

EARLY FORMS OF BOILERS 

The earliest boilers of which we have reliable record were spher- 
ical. They were of cast iron and set in brickwork. It was custom- 
ary to set this type of boiler with the fire underneath and construct 
flues in the brickwork to conduct the hot gases around the boiler just 
below the water level. The hot gases passed entirely around the 
boiler before escaping to the chimney. 

Haystack Boiler. The next form to be generally used was that 
invented by Newcomen in 1711. On account of its peculiar shape 



6 



TYPES OF BOILERS 



it was called the "Haystack" or "Balloon" boiler. It was of wrought 
iron and had a hemispherical top and arched bottom. The fire was 
placed underneath the arched portion, the hot gases surrounding 
the lower part of the boiler. An improved form of the Haystack 
boiler is shown in Fig. 1. Smeaton placed the fire inside the shell 
and arranged internal flues for conducting the hot gases to the 
chimney. This arrangement increased the heating surface and, 
consequently, the economy of the boiler. 

Wagon Boiler. To increase 
the heating surface still more, 
James Watt introduced his 
"Wagon" boiler, Fig. 2. The 
top was semicylindrical and the 
sides curved inward. The curved 
plates assisted in the formation 
of side flues. The hot gases 
passed from the grate beneath 
the boiler to the rear, through 
the left-hand flue to the front, 
then through the right-hand flue 
to the rear, and thence to the 
chimney. This was called the 
"wheel draft" because the gases 
passed entirely around the boiler. 
In the large sizes a flue was 
placed in the boiler. The prod- 
ucts of combustion returned 
through this flue to the front after passing under the boiler to the 
rear, as in the small sizes. On issuing from the flue at the front, 
the gases divided and passed to the chimney at the rear by means 
of the flues in the brickwork. This form of draft was called the 
"split draft". 

Watt used a column of water in the vertical feed pipe as a pres- 
sure gage; the rise and fall of this column also controlled the damper. 
The feed was regulated by a float. 

Although such boilers as the Haystack, Wagon, and others were 
fairly satisfactory at the time they were invented, they could not 
withstand the higher pressures which soon became common. 




Fig. 1. The Haystack Boiler 



TYPES OF BOILERS 7 

About the beginning of the nineteenth century the cylindrical 
boiler was introduced. The earliest forms were the plain cylin- 
drical boiler and the "egg-end" boiler. The difference was in the 
form of the ends— those of the former were flat and of cast iron, 
while the ends of the latter were hemispherical and made of wrought 




Fig 2. Diagrammatic Sketch of Watt's "Wagon" Boiler 

iron. The egg-end boiler required no staying or bracing because its 
form is, with the exception of a sphere, the strongest to resist internal 

pressure. 

Cylindrical Boilers. The cylindrical boiler consists of a shell of 
wrought-iron boiler plate and ends of the same material or of cast 



8 



TYPES OF BOILERS 



iron. It is set in brickwork as shown in Fig. 3. The boiler is about 
two-thirds filled with water, the remaining third forming the steam 
space. To collect and store the steam as it rises from the water a 
steam dome is added. The steam pipe is attached to the dome, to 
which the safety valve is connected also. The hot gases from the 
fire pass under the boiler to the rear and then to the chimney. 

The heating surface of this type is small for a given diameter 
unless the boiler is very long. As all sediment collects in the bottom 
where the heat is most intense, the plates are likely to be burned. 
Sediment and scale being poor conductors of heat, the heat remains 
in the plates and burns them instead of passing to the water. 







Fig. 3. Cylindrical Boiler and Setting 



The disadvantages — the small heating surface and the collec- 
tion of sediment — do not seem so serious when the simplicity, dura- 
bility, and strength of construction, and the ease of cleaning and 
making repairs are considered. 

The plain cylindrical boiler is adapted for mining districts and 
other places where fuel is abundant and where skilled boilermakers 
are not readily found. This boiler is made very long to obtain the 
required heating surface, the length sometimes exceeding fifty feet. 
Some of these boilers are still in use where relatively low operating 
pressures are allowed, but they are being rapidly displaced. 



TYPES OF BOILERS 



MODERN FLUE 
BOILERS 

In order to get the 
necessary heating surface 
in the cylindrical boiler 
without making it exces- 
sively long, it was made with 
an internal flue through 
which the hot gases passed 
to the chimney. This flue 
was quite large and ex- 
tended from end to end of 
the boiler. In the United 
States, Oliver Evans used 
this type as early as 1800. 
In England, it led to the 
internally-fired flue boilers 
which were, and are still, 
extensively used. 

CORNISH BOILER 
Horizonta 1 — Single- 
Flue — lnternally=Fired. 

When it was found that a 
large proportion of the total 
heat of combustion was lost 
by radiation and air infil- 
tration, a Cornish engineer 
named Trevithick conceived 
the idea of placing the fire 
inside of a large internal 
flue. The type he intro- 
duced is known as the Cor- 
nish boiler. 

Path of Hot Gases. 
The products of combustion 
pass from the fire on the 
grate bars C, Fig. 4, through 




- 

X 

e 

O 

o 

c 






10 



TYPES OF BOILERS 



the flue to its back end, where they divide and return to the front 
end by means of the lateral flues L in the brickwork. At the 

front the hot gases pass downward and, unit- 
ing, pass through the flue F in contact with 
the bottom of the boiler. On leaving the 
boiler they go to the chimney. This arrange- 
ment of flues reduces the temperature of 
the gases before they come in contact with 
the bottom of the boiler, where sediment 
collects. The grate bars rest on the dead plate D at one end and on 
the bridge B at the other, Fig. 4. If made in two lengths, as is often 
the case, they are supported at the center by a cross bearer. The 
bridge is built of fire brick, and the external flues are lined with fire 
brick. The heads are stayed to the shell by gusset stays EE. 




Fig. 5. Adamson Ring Fur- 
nace Construction 



*-Insidedia4/ — 



5 e Safety Valve 




y/////«ri 



Fig. 6. Section of Morison Boiler Showing Corrugated Flue 
Courtesy of Joseph T. Ryerson & Son, Chicago 

Taking Care of Expansion. The large internal flue is the 
hottest part of the boiler because it contains the fire. For this 
reason the flue has greater linear expansion than the shell, and, when 






TYPES OF BOILERS 11 

the flue is a plain cylinder, the increase in length causes the ends to 
bulge. When the boiler is cold, the flue returns to its normal length. 
This lengthening and shortening will soon loosen the flue at the 
ends. To overcome this, the flue is sometimes made up of several 
short rings flanged at the ends and joined by being riveted to a plain 
ring. This construction is shown in section in Fig. 4. Another 
method is shown in section in Fig. 5. The plain rings are riveted to 
the curved rings; the latter take up the expansion, slightly increase 
the heating surface, and strengthen the flue against external pres- 
sure. This form is known as the "Adamson Ring". The same 
results may be obtained by the use of the corrugated flue, one form 
of which is shown in Fig. 6. The corrugated flue has many advan- 
tages over the devices shown in Figs. 4 and 5; it is frequently used 
in internally-fired boilers. 

LANCASHIRE BOILER 

Horizontal — Two=FIue — Internally=Fired. It can be proved, 
both by experiment and by calculation, that with a given thickness 
of material cylinders of large diameter cannot withstand as much 
pressure as smaller ones. For this reason, and on account of the 
short distance a fireman can throw coal accurately, the Cornish 
boiler is suitable for small powers only. If it is made too large, the 
flue is likely to collapse; but, on the other hand, if the diameter of 
the flue is too small, the grate will be insufficient in area. When 
this form of boiler is to be used in a large size, it is modified by using 
two flues instead of one. This is called the Lancashire boiler. It 
is like the Cornish except that it has two flues and, of course, two 
furnaces. 

The flues are sometimes continued separately to the end. If 
they merge into one large flue, which forms the combustion cham- 
ber, it is called the "breeches-flued" or duplex furnace boiler. These 
furnaces are fired alternately; the unburned gases set free from the 
freshly-fired coal are burned on meeting the hot gases from the 
incandescent coal of the other furnace. This arrangement aids in 
preventing the escape of partly burned gases. 

The main disadvantage in the design of the Lancashire 
boiler is the difficulty in finding room for the two flues without 
greatly increasing the diameter of the boiler. Also, the small furnace 



12 



TYPES OF BOILERS 



space is unfavorable to the complete combustion of the gases, the 
space for mixing and burning being restricted. The combustion 
chamber of the breeches-flued boiler increases the space, but the 
construction at the junction of the two flues is weak and has been 
responsible for many explosions. 

GALLOWAY BOILER 

Horizontal — Two=Flue — Internally=Fired — Galloway Tubes. 

Another boiler of the same general form is the Galloway, shown in 
Figs. 7, 8, and 9. It was developed with a view to overcoming the 




Fig. 7. Galloway Boiler. Brick Setting Partially Removed 

shortcomings of the Lancashire boiler by providing obstructions in 
the flues to cause an intimate mixture of the gases of combustion, at 
the same time adding efficient heating surface; the cross flues also 
serve to create a circulation of water around the bottoms of the 
main flues, thus overcoming a serious objection to the Lancashire 
boiler, which is deficient in this respect. 

Two Types. There are two different forms of Galloway boilers : 
those having two distinct flues, and those having two furnaces 



TYPES OF BOILERS 



13 



which unite into one large flue. The earlier form has two flues 
extending the length of the boiler; behind the furnace short tubes, 
as shown in Fig. 8, cross the flues. 

In the later form, the two flues merge 
into one large flue of the shape shown in 
Fig. 9. This flue has corrugated sides 
and the conical tubes are staggered, thus 
insuring a thorough breaking up of the 
currents of hot gases. The tubes are 
made conical to facilitate removal for 
repairs. The shape of the tube also per- 
mits the water to expand on being 
heated, and the particles to rise vertically 
without disturbing the water on the heating surfaces above. The 
conical tubes are more generally riveted than welded because 
the removal of a tube that is welded leaves a large hole in 
the flue. This form of flue boiler marked a big advance over 
the earlier forms, partly due to the inherent improvements 




Fig. S. Cross Flues in Two-Flue 
Galloway Boiler 




Fig. 9. Later Form of Galloway Flue 



and partly because the manufacturers realized the importance 
of related features, such as skillful firing and providing adequate 
draft. Many of these boilers are still in use in America as well as 
in England. 



14 



TYPES OF BOILERS 



FIRE-TUBE BOILERS 



COMMON HORIZONTAL TYPE 
Single=Flue Boiler. Single Fire Tube — Externally-Fired. In 
the Cornish, Lancashire, and Galloway boilers, the large internal 
flue served as a fire box. There was, however, a flue boiler having 
the fire external to the shell. The boiler shown in Fig. 10 resembles 
the plain cylindrical boiler, illustrated by Fig. 3, both in appearance 
and setting, but it has one or more large flues extending from end to 
end. This increases the heating surface to such an extent that the 
boiler can be considerably shorter than the plain cylindrical ^boiler. 
Note that the gases leave the setting on the front end. 




Fig. 10. Section of Cylindrical Flue Boiler 

Multitubular Boiler. Many Small Fire Tubes— Externally- 
Fired. When engineers found that the internal flue was an advan- 
tage, they soon added more tubes. As the number increased, the 
size diminished until they became of the size used at present. This 
is a brief statement of the development of the multitubular boiler. 
For many years this type of boiler has been commonly used for 
stationary work, and, although other types possess advantages for 
certain conditions, it is still considered economical, reliable, easily 
handled, and safe, if constructed of good material and operated 
with care and intelligence, in small and medium-sized plants oper- 
ated at moderate pressures. 



TYPES OF BOILERS 



15 



Description. Figs. 11 to 14 are selected to illustrate this boiler. 
The boiler without the brick setting is shown in Fig. 11. It consists 
of a steel cylindrical shell and numerous small tubes extending from 
end to end. These tubes are 3 to 4 inches in diameter and are 
fastened to the two ends, called tube sheets, by expanding the 
tubes into the sheet and beading them over on the outside. The 
shell is made of steel plates i to f inch in thickness, depending on 
the diameter and pressure. At the front, the shell plates extend 
beyond the tube sheet and are cut away to allow the waste gases to 
enter the uptake. About one-third the volume of the boiler is 
occupied by the steam; the other two-thirds is filled with water and 
tubes. The water line is a short distance (from 3 to 8 inches) above 
the top row of tubes. 




Fig. 11. Multitubular Boiler without It3 Setting 

The flat ends are prevented from bulging by stays, which may 
be of the form shown in Fig. 12, or they may be diagonal stays. 
The through stays are fastened to the tube plates by means of nuts 
and washers as shown at S in Fig. 11, and also in Fig. 12. Below 
the water level, the end plate is stayed by the tubes. This type of 
boiler may be supported by brackets B riveted to the shell or by 
means of beams and columns, as shown in Fig. 14. The front 
bracket is often fixed in the side wall, but the rear bracket should 
be placed on rollers. This will prevent the straining of the plates 
during expansion and contraction. A small space must be left 
between the rear tube sheet and the brick wall to allow for 
expansion. 



16 



TYPES OF BOILERS 



. 



Ol. 



The boiler shown in Fig. 11 has two steam nozzles N. If the 
boiler has a dome, the steam nozzle is placed either at or near the 

top of the dome. The feed 
pipe may enter either at the 
front or at the rear. It fre- 
quently terminates in a per- 
forated pipe below the water 
line. The blow-off pipe is at 
the rear of the boiler, as 
shown in Fig. 13. A valve, 
called the blow-off valve, reg- 
ulates the flow and may be 
opened to blow out sediment 
and detached scale. The 
boiler is usually set with a 
slight inclination toward the 
rear so that mud and detached 
scale may collect near the 
blow-off pipe. 

Cleaning and Repairing. 
In order that the boiler may 
be entered for cleaning or 
repairs, it is provided with 
manholes and handholes. Fig. 
11 shows a manhole M at the 
top near the middle and a 
handhole near the bottom of 
the front tube sheet. Hand- 
holes may be put in wherever 
desired, but manholes can be 
located only where the ar- 
rangement of stays and 
tubes will permit a space large 
enough for the entrance of a 
man. Manholes and hand- 
holes are made elliptical in 
shape. The former are about 11 inches by 15 inches in size, and 
the latter about 4 inches by 6 inches. 



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TYPES OF BOILERS 



17 



Heating Surface. The heating surface is the surface exposed 
to hot gases. In this type, the heating surface is made up of 




about half the shell, the tubes, and about two-thirds of the rear tube 
sheet. In general, all the heating surface is below the water line. 



18 



TYPES OF BOILERS 



Form of Setting. The complete multitubular boiler is shown in 
its brick setting in Fig. 14, and a longitudinal section of the setting 
in Fig. 13. The brick setting consists of brick laid in cement or 
mortar. The bridge and the portions of the furnace exposed to the 
fire are lined with fire brick, laid in fire-clay mortar. The bridge is 
built at the rear of the grate and forms a support for the grate bars; 
it also directs the flames upward. The arrows show the direction 
of the flow of hot gases. The furnace is formed by the bridge, the 
side walls, and the lower part of the boiler front. The boiler front 
is usually of cast iron with the lower part lined with fire brick. 

The front has doors which lead to the 
furnace, ash pit, and smoke box. The 
space below the grate is called the ash 
pit, and through its doors ashes are 
removed and a large portion of the air 
for combustion enters. Both the fire 
doors and the ash-pit doors have draft 
plates, or grids, to regulate the supply 
of air. The doors to the smoke box 
give access to the tubes for cleaning 
and repairs. 

VERTICAL TYPE 

Upright boilers are used when 
floor space is valuable and there is 
sufficient height. Small sizes are 
used for pile driving, supplying steam 
for pumps and similar work, and in 
hoisting engines; large sizes are used 
if it is necessary to have a powerful 
battery in a small space. In general, 
they are not so economical as horizontal multitubular boilers unless 
they are carefully designed and of considerable height. If the tubes 
are short, the hot gases escape before they give up much of their heat. 
Single=Tube Boiler. One of the simplest forms of upright 
boiler is shown in Fig. 15. It has a cylindrical shell with a large 
fire box at its lower end. This fire box is formed by the inner cyl- 
inder, which is fastened to the outer shell by short screw stay bolts 




Fig. 15. Vertical Fire-Box Boiler 



TYPES OF BOILERS 



19 



as shown. A flanged ring connects the fire box with a large flue 
which conducts the hot gases away. The necessary handholes, 
gages, safety valves, etc., are provided. This form is not econom- 
ical but is used on account of the little attention required. 

Multitubular Boiler. More economical forms of the small 
upright boiler are illustrated in Figs. 16 and 17. The boiler shown 
in Fig. 16 is a common form, externally being like the boiler repre- 
sented by Fig. 15, but having a somewhat different inside construc- 





Fig. 16. Vertical Multitubular Boiler 



Fig. 17. ^ Vertical Multitubular Boiler 

with Upper Ends of Tubes Below 

Water Line 



tion. It resembles a multitubular boiler placed on end. The fire 
box is made of an inner cylinder stayed to the outer. The top of 
the fire box, called the lower tube sheet, is connected to the upper 
head by tubes, through which the hot gases pass to the smoke pipe. 
It will be readily seen from Fig. 16 that the upper ends of the tubes 
are surrounded by steam while the lower portions are covered 
with water. As steam is a poor conductor of heat, the ends of these 
tubes are liable to injury from overheating. 



20 



TYPES OF BOILERS 




Fig. 18. Manning Boiler 
Courtesy of The Bigelow Company 



In the class of boiler shown in 
Fig. 17 the upper ends of the 
tubes are below the water level, 
thus avoiding the fault just 
described in connection with Fig. 
16. The upper tube sheet is 
submerged, and is flanged and 
riveted to the frustrum of the 
cone which forms the smoke box. 
The chief defect in this boiler is 
that the lower part of the cone 
is often placed too near the shell; 
this is done to admit more tubes. 
This construction restricts the 
space so much that there is not 
sufficient room for the steam to 
rise as it is formed on the tubes. 
The cone, which is subjected to 
external steam pressure, is likely 
to be weak and should be care- 
fully stayed. 

These small upright boilers 
require no brick setting, as the 
fire box is within the boiler and 
the cast-iron foundation forms 
the ash pit. 

Manning Boiler. The Man- 
ning boiler is illustrated in Fig. 
18. It is, in general, similar to the 
upright boiler shown in Fig. 16, 
but in order to get a large heat- 
ing surface, it is made 20 to 30 
feet high. At the lower portion, 
the shell is of greater diameter 
than at the top in order to pro- 
vide a large grate area. The 
inner fire box is stayed to the 
shell by screw stay bolts. As 



TYPES OF BOILERS 



21 



the fire box is surrounded by water and there are many long tubes, 
there is a large heating surface. The tubes are arranged in concen- 
tric circles with a space for circulation in the middle. 

The external fire box is joined to the shell by a double-flanged 
ring as shown in Fig. 19; or by the cone-shaped section as illustrated 
in Fig. 20. The top edge of the internal fire box is riveted to the 
lower tube sheet, which is flanged. The bottom of the inner fire 




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Fig. 19. Manning Boiler Details 




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Fig. 20. Manning Boiler Details 




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box is connected to the outer shell by a welded ring, shown in section 
in Figs. 19 and 20, called the foundation ring. The water space 
between the inner and outer fire-box plates, called the water leg, 
should be large. 

This boiler is cleaned by means of handholes. They are placed 
in the shell plates near the lower tube sheet, in the external fire box 



22 TYPES OF BOILERS 

just over the furnace door, and at the bottom near the foundation 
ring. As there are no manholes for cleaning, the boiler is suited to 
good feed water only. 

The feed pipe enters the shell at the side near the middle of the 
water space, and extends across the boiler; it is perforated to dis- 
tribute the water. 

The heating surface consists of the inside of the fire box and the 
tubes up to the water level, and the tube sheet. That part of the 
tubes above the water line is the superheating surface; that is, the 
heat from the gases passes through the metal of the tubes to the 
steam, thus raising its temperature without raising its pressure. 
Steam heated under these conditions is called "superheated steam". 
In small vertical boilers this superheating surface is not desirable 
because the work of the small boiler does not require superheated 
steam and the tubes are likely to be burned by the intense heat. 
With the long tubes of the Manning, the gases are not as hot when 
they reach the top, and as this boiler is built in fairly large sizes, 
200 horsepower being common, the engines supplied are built for 
economy, and require dry if not superheated steam. 

INTERNALLY=FIRED MARINE TYPE 

RETURN=TUBULAR BOILERS 

Horizontal — Many Small Fire Tubes. The boilers hitherto 
described are used mainly for stationary work, the exceptions being 
so few that they need not be even mentioned. However, there is 
another modification of the fire-tube boiler which is now extensively 
used in marine work. The parts of the return-tubular boiler are 
essentially the same as those of flue boilers (Cornish and Lancashire) 
and of the multitubular boiler. They are, however, arranged 
differently in order to be used on board ship. 

Earliest Forms. The earliest forms of marine boilers, working 
with pressures of 15 to 30 pounds per square inch, were square or 
box-shaped. They were economical and of convenient form for 
ships. When higher steam pressures became necessary, the flat 
surfaces required so much staying that they were abandoned and 
the cylindrical type was introduced, as this form is the best of the 
practical shapes to resist internal pressure. The cylindrical form 



TYPES OF BOILERS 



23 



may not be as conveniently stowed aboard ship, but it will stand 
much higher pressures. The cylindrical marine boiler is frequently 
built for 200 pounds per square inch working pressure. 

Single=Ended Single=Flue Type. The single-ended return- 
tubular boiler, shown in Fig. 21, combines the internal furnace flue 
of the Cornish type and the numerous small fire tubes of the multi- 
tubular. The cylindrical shell is made up of plates riveted together 
and to the flat ends of the boiler, which are flanged to fit the shell. 

Furnace. The furnace is cylindrical, 3 to 4 feet in diameter, 
and about 7 feet in length. The front end of the furnace flue is 
riveted to the front end plate, which is flanged for the purpose. 
The back end is riveted to the combustion chamber plates. For- 




SH£US 

Fig. 21. Return-Tubular Boiler. Early Form 



merly, the flue was a plain cylinder, but as a plain cylinder, unless 
of small diameter, cannot stand much external pressure, it soon 
became necessary to strengthen it. This was done by means of the 
curved ring shown in Fig. 5 and other methods; at present the 
corrugated flue is used, one form being shown in Fig. 6. 

Grate. The grate is placed at about the center of the height of 
the furnace flue; the space above this grate is occupied by the fire 
and hot gases, while below is the ash pit. As will be seen from the 
arrows in Fig. 21, the hot gases fill the space above the fire, the 
combustion chamber, the tubes, and the uptake. 

Combustion Chamber. The combustion chamber, in which the 
products of combustion are burned, is formed of flat and curved 



24 



TYPES OF BOILERS 



plates flanged at the edges and riveted together. The shape of the 
plates is shown in Fig. 21, which is a sectional view of a single-ended 
marine boiler. The back tube sheet forms the front of the combus- 
tion chamber. The space around the tubes, furnace flue, and com- 
bustion chamber is filled with water, the water level being 6 to 8 
inches above the top row of tubes. The space above the water 
level is called the steam space. 

Stay Rods. As the return-tubular boiler has several flat surfaces, 
this type requires careful staying. The flat ends above the water 




Fig. 22. Return-Tubular Boiler with Three Flues 



level are prevented from bulging by long stay rods similar to those 
in the multitubular type. Below the water level, the furnace flue 
and the tubes aid in holding the flat plates in position. Moreover, 
a few of the tubes, shown by the heavier circles in Fig. 21, are made 
thicker so that a thread may be cut on the ends, which are screwed 
into the tube sheets and held by thin nuts. The combustion cham- 
ber plates are stayed to the rear end plate and the shell by short 
screw stay bolts. The flat top of the combustion chamber is sup- 
ported by girders or crown bars. 




TYPES OF BOILERS 



zo 



Single=Ended Multiple=Flue Type. The boiler shown in Fig. 
21 has only one furnace, but return-tubular boilers frequently have 
two, three, or four furnaces. 

Fig. 22 shows a boiler with three furnaces. Large furnaces are 
more efficient than small ones because the grate area increases 
directly as the diameter, while the air space above the grate increases 
as the square of the diameter. The greater space aids combustion. 
The length of the grate bars is nearly constant for all sizes of flue 
because it is limited by the distance a fireman can throw coal. Fur- 
nace flues are usually from 36 to 54 inches in diameter. As the 
size of furnaces is fixed, the number depends upon the size of the 
boiler, for a large boiler must have a large grate area, which can be 
obtained only by using several furnaces. The various arrange- 
ments are shown diagrammatically in Fig. 23. 



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Figo 23. Several Arrangements of Multiple-Flue Boiler Tube Sheets 



Arrangement of Combustion Chambers. A single-furnace boiler 
has but one combustion chamber. A two-furnace boiler may have 
a combustion chamber for each furnace or it may have a common 
combustion chamber. It is better to have a common combustion 
chamber for the two furnaces, because alternate stoking keeps 
up a more nearly constant pressure of steam and there is less smoke. 
Three-furnace boilers usually have three combustion chambers, 
while four-furnace boilers have two. In case four furnaces are used 
with three combustion chambers, the two center furnaces lead to a 
common combustion chamber and each outside furnace has one. 

Double=Ended Type. This form of marine return-tubular boiler 
is practically the same as two single-ended boilers placed back to 
back, but with the rear plates removed. The weight of the rear 
plates is saved, and there is less loss from radiation. This makes 
the double-ended boiler lighter and cheaper in proportion to the 



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TYPES OF BOILERS 



27 



heating surface. Double-ended boilers are often made 16 feet in 
diameter and IS feet long. 

There are two distinct classes of double-ended return-tubular 
boilers — those having all the furnaces open into one combustion 
chamber and those having 
several combustion chambers. 
The boiler having but one 
combustion chamber has the 
disadvantage that if one fire 
is being cleaned the whole 
boiler may be cooled by the 
inrush of cold air. It is better 
to have a combustion cham- 
ber for each furnace, or at 
least to have a combustion 
chamber for the furnaces of 
each end. The usual method 
of dividing up the combus- 
tion chambers is by water 




spaces, as shown in Fig. 24 
which shows sections of a boiler 
having a combustion chamber 
for each furnace. 

Stationary Return=Tubu= 
lar Type. While the return- 
tubular boiler is commonly 
used in marine work, this type, 
with some changes in detail, is 
used in stationary plants. Fig. 
25 shows the construction and 
arrangement of parts. The 
flue is larger in proportion to 
the diameter than is the case 
with the marine form; the 
combustion chamber is partly external to the shell; that is, the 
rear tube sheet is also the rear end plate. This arrangement does 
away with the necessity of staying the flat plates of the combustion 
chamber. 



28 



TYPES OF BOILERS 



Another form of internal-furnace return-tubular boiler is shown 
in Fig. 26. This boiler usually has two flues extending from the 
front to the back head. The grate is placed in the corrugated 
portion, while conical water tubes support the flue back of a bridge 
wall. The large furnaces and the space around the conical tubes 
provide a combustion chamber of ample size. 

The arrows show the direction taken by the hot gases. After 
leaving the internal flue they enter the return tubes, which are below 
the furnace; before leaving the boiler, they pass underneath the 




OUTLET 

Fig. 26. Stationary Boiler of the Return-Tubular Type 



shell. By this arrangement the hotter gases are near the water line 
and the cooler gases in contact with the cold water. Thus there is 
the greatest difference in temperature at all times. At each change 
in the direction of the hot gases, there is an opportunity for dirt 
and ash to fall by gravity, so that the tubes may remain clean and 
efficient. 

With the exception of the foundation there is no brickwork. 
The shell is covered with a non-conducting material. This boiler, 
like the Galloway, has a large steam and water space, thus insuring 
dry steam and great reserve power. 



TYPES OF BOILERS 



29 



THROUGH=TUBE BOILERS 

Horizontal — Many Small Fire Tubes. Vessels of light draft 
require a boiler of small diameter. This is especially true of gun- 
boats, as it is desirable to have the boilers below the water line. As 
there is not room for the return-tubular boiler, the through-tube, 
shown in Fig. 27, is sometimes used. This boiler is made up of the same 
parts as the return-tubular, the chief difference being that of arrange- 
ment. The rear plate of the combustion chamber forms one tube 
sheet and the end plate forms the other. The top of the combustion 
chamber is stayed to the shell by sling stays, which are bars having 
forked ends fastened to the shell and to the combustion chamber. 




Fig. 27. Through-Tube Boiler. Longitudinal Section 

The fire is in a flue, or flues, which leads to the combustion 
chamber. The hot gases pass from the combustion chamber through 
the tubes to the uptake at the back end. The chief objection to 
this form is its length, for the heating surface is small unless the 
boiler is made very long. 

FIRE-BOX TYPE 

LOCOMOTIVE BOILERS 
Horizontal — Small Fire Tubes — Externally=Fired. Although 
vertical fire-tube boilers may be classed as fire-box boilers, yet the 
name fire-box boiler is usually applied to the locomotive type whether 
used with a locomotive or as a stationary boiler. 



30 



TYPES OF BOILERS 



The usual form of horizontal fire-box boiler consists of a cylin- 
drical shell, or barrel, partly filled with tubes, and a rectangular fire 
box. The shell is prolonged beyond the rear tube sheet to form a 
smoke box. The front ends of the tubes open into the fire box, 
while the rear ends open into the smoke box. The hot gases from 
the fire pass through the tubes to the smoke box, and thence to the 
stack or uptake. For locomotive work, there is a large number of 
small tubes, usually 2-inch, but for stationary work the tubes are 
larger and less numerous. The reason for this difference is that in 
the locomotive boiler a greater heating surface is necessary, and to 
obtain sufficient draft to burn the large amount of coal for this 




Fig. 28. 



Locomotive Fire-Box Boiler Showing Tube Across Fire Box to Support Tile for 
Furnace Arch 



heating surface, the exhaust steam is turned into the smoke box. 
The blast of steam carries the heated gases up the stack and a fresh 
supply of air passes through the grate. 

The cylindrical shell is joined to the fire box by riveting to a 
flanged ring or to a cone-shaped portion, as in the vertical boiler. 
The fire box has a rectangular cross section and usually a flat top. 
Like the vertical boiler, there is an inner and an outer shell for the 
furnace, the inner having the same shape as the outer, except that 
the top is flat. The external shell is connected to the inner by short 
screw stays. The space between is called the water leg. The flat 
top is stayed by girders or crown stays. These are sometimes 
attached to the shell by sling stays. The lower portions of the tube 



TYPES OF BOILERS 



31 



sheets are held ir place by the tubes; the upper portions are stayed 
by diagonal stays. 

The chief differences in 
the various forms of locomo- 
tive boilers are the shape of 
the fire box and the location 
of the grate. Locomotive boil- 
ers are either straight top or 
wagon top. The wagon top 
boiler, Fig. 28, has a cone- 
shaped portion by means of 
which the boiler is larger at 
the fire-box end. This con- 
struction is to give a greater 
steam space. The increase in 
size of boilers has raised the 
top so high above the rails that 
the wagon top is not now used 
extensively; the straight top, 
Fig. 29, is more common. 

Belpaire Boiler. The 
shell and fire tubes of this 
type of boiler are practically 
the same as in any other fire- 
box boiler; the peculiarity lies 
in the fire box. The inner and 
outer fire-box plates are hori- 
zontal at the top, and the sides 
of the outer fire box are con- 
tinued so that the space above 
the crown sheet is rectangular 
in section. The advantage to 
be gained by this construction 
is that the stay bolts, which 
hold the crown sheets and side 
sheets, can be placed at right 

angles to the sheets. This reduces any tendency on the part of the 
sheets to bend when under pressure. 




TYPES OF BOILERS 



33 



Wootten Boiler. In this type, also, the fire box is the chief 
part to be considered. The size of the locomotive fire box is 
limited. With older types the width was limited to less than 3 
feet and the length to less than 7 feet. This was because of the 
frames and the distance between the axles. By placing the fire 
box above the axles, the width was increased by an amount equal 
to the thickness of the frames, or about 7 inches, and the length 
increased to about 11 feet. By the method of supporting the fire- 
box end of the boiler on trucks, the width can be still further 
increased. 

Fire Box. A broad, shallow fire box is required if anthracite 
coal is used. The Wootten fire box, shown in Fig. 30, is very 




Fig. 31. Lentz Locomotive Fire-Box Boiler 

wide and is placed on top of the driving wheels. Formerly, a 
combustion chamber was placed between the end of the grate 'and 
the tubes, but, as it was found to be unnecessary, it is not now used. 
Lentz Boiler. The object of the design shown in Fig. 31 is to 
avoid the use of stays. To do this, no flat plates are used except 
the tube sheets, and these are stayed by the tubes. The fire box is 
in the form of a corrugated flue similar to those in internally-fired 
return-tubular boilers. As this is circular it requires no stays. The 
shell is circular and shaped as shown in the illustration. This type 
has been much used in Europe, but only a few have been built in 
this country. 



34 



TYPES OF BOILERS 



STATIONARY BOILERS 
General Fire=Box Type. The fire-box boiler, usually called 
the locomotive boiler, is often used for stationary work, traction 
engines, and for vessels of light draft. This type of boiler, slightly 
modified, is sometimes used for generating the steam for heating 
buildings. It is economical and durable when used with natural 
draft. The chief differences in construction are larger tubes because 
of the draft, and the changes due to method of support. A common 




Fig. 32. Locomotive Type of Boiler for Stationary Use 

form is shown in Fig. 32. This type has been built in large sizes 
for high pressure, but when so made is expensive. 

PECULIAR FORMS 
Return=Tubular Fire=Box Boiler. Boilers of the form shown in 
Fig. 33 resemble the locomotive fire-box type, but in addition have 
return tubes. The hot gases reach the uptake by means of these 
tubes instead of passing to the chimney from the smoke-box end. 
Thus they combine the advantages of the fire-box type and the 
return-tubular type without the brick setting. The water surrounds 
the furnace on all sides except the front. They are built in sizes 
from 12 to 70 horsepower. As Fig. 33 shows the construction so 
clearly, further description is unnecessary. 



TYPES OF BOILERS 



35 



Cochrane Vertical Boiler. The Cochrane vertical boiler is 
somewhat like the return-tubular boiler in point of arrangement of 




Fig. 33. Locomotive Fire-Box Return-Tubular Boiler 

heating surface. This boiler is shown in section in Fig. 34. The 
hot gases pass from the furnace to the combustion chamber, then 
through the tubes to the uptake. 
The heating surface consists of 
tubes and the plates of the fire 
box, which is surrounded by 
water except at the bottom. The 
crown of the boiler and of the 
fire box, being hemispherical, 
require no staying. The hemi- 
spherical crown also allows a large 
steam space. The flat plates (the 
tube plates) are held together by 
the tubes. 

Shapley Boiler. The Shap- 
ley boiler, shown in Fig. 35, may 
be called a return-flue vertical 
boiler. The upper portion is a 
reservoir for water and steam, and 
the lower contains the fire box. 

The CrOWn sheet Of the fire box is Fig , 34. Cochrane Vertical Boiler 




36 



TYPES OF BOILERS 



stayed to the top by through stays. The hot gases from the fire rise 
in the fire box and pass through short horizontal tubes to an annu- 
lar space. This annular space is connected to the flue at the base 
by vertical tubes passing through the water space. 

This boiler has a large combustion chamber; the fire box is 
surrounded by water, and the crown sheet and tubes are removed 
from the intense heat of the fire. This arrangement increases the 




Fig. 35. Section of the Shapley Vertical Boiler 



heating surface, allows good combustion, and results in a durable 
boiler. The base is partly filled with water, so that any sparks 
carried over will be quenched. 

Brady Scotch Boiler. The Brady Scotch Boiler, Fig. 36, is a 
modification of the well-known standard marine boiler, and com- 
bines the advantages of internal firing with some virtues of its own. 
The lower shell contains two corrugated flues, one being shown in 
part section in the figure; the flues lead into a chamber at the back 



TYPES OF BOILERS 



37 



of the shell from which a large number of fire tubes extend 
over the flues, thus leading the heat to the stack at the front 
of the boiler. The upper drum, which is connected to the lower 
shell by large necks at front and rear, is kept about one-third full 
of water. 

In the Brady boiler, positive circulation is obtained by an 
annular ring placed around the inside of the shell, with an opening 




Fig. 36. Section of Brady Scotch Boiler 
Courtesy of International Engineering Works, South Framingham, Massachusetts 

at the bottom. (Shown by white line and arrows curving upward at 
bottom of Fig. 36.) As the front neck of the upper drum leads into 
the annular space the water is compelled to pass around the shell to 
the base of the boiler, w T here it rises around the flues and between 
the tubes to the rear, back of the upper drum as shown by the arrows 
in Fig. 36, thus establishing the proper circulation and overcoming 
a difficulty in Scotch marine boilers which sometimes have poor 
water circulation. 



38 



TYPES OF BOILERS 



The Brady boiler, being internally-fired, requires no brick 
setting and, as the hot gases in the flues and tubes are at all times 
surrounded by water, the losses from radiation are reduced to a 
minimum. Standard manholes and handholes are provided, allow- 
ing a thorough inspection and cleaning of all parts of the boiler 
without difficulty. The boilers are suitable for both marine and 
stationary work. 

Directum. The Begg's "Directum" boiler, Fig. 37, is, in 
brief, a horizontal, externally-fired, return-tubular boiler in which 
tubes conduct hot gases through the space behind the bridge. This 




Fig. 37. "Directum" Externally-Fired Return-Tubular Boiler 
Courtesy of James Beggs and Company, New York City 

boiler consists of a shell partly filled with 3-inch tubes. The rear 
of the furnace is a throat sheet in which 4-inch tubes are expanded. 
The other ends are expanded into the rear end plate, which is made 
large enough for the purpose. The furnace is encased in steel 
plates lined with fire brick held in place by rods passing through 
the notches as shown. The manhole for entering the boiler is 
placed in the front head instead of in the shell, as is frequently done. 
A number of other makes of this type of boiler have been devel- 
oped. The "Economic", Fig. 38, manufactured by the Erie City 
Iron Works, Erie City, Pennsylvania, is a notable example. 






TYPES OF BOILERS 



39 




Fig. 38. "Economic" Directum Boiler 
Courtesy of Erie City Iron Works 

WATER=TUBE BOILERS 

General Characteristics. Water-tube boilers differ essentially 
from fire-tube boilers, the names indicating the chief points of differ- 
ence. In the fire-tube boiler, the tubes, which are surrounded by 
water, conduct the hot gases to the smoke box. In the water-tube, 
the tubes are filled with water, and the hot gases pass over and 
among them on their way to the chimney. 

Although flue boilers and the tubular types were introduced at 
an earlier period than the water-tube, yet the last-named type is 



40 



TYPES OF BOILERS 



not a new form of steam generator. About a century ago, John 
Stevens invented a water-tube boiler and fitted it to a steamboat. 
This boiler, Fig. 39, was a combination of small tubes connected at 
one end to a reservoir. Thus the "Porcupine" was one of the earli- 
est forms. At various times since then many ideas have been 
worked out both for marine and stationary boilers. During the 
last twenty-five years, however, the water-tube boiler has been 
steadily growing in favor, the chief reasons being the necessity of 
higher steam pressures, larger capacities, greater reliability of mate- 
rials, greater skill in design and workmanship, and more intelligent 
management. 

It is not within the province of this article to discuss the 
relative merits of fire-tube and water-tube boilers, but a careful 




Fig 39, Diagrammatic Sketch of Stevens Boiler 



impartial consideration seems to show that as far as economy of 
running is concerned there is but little difference, providing condi- 
tions exist permitting the use of either type. The fire-tube boiler 
is reliable and can be handled by those possessing comparatively 
little knowledge of engineering; its chief defect seems to be the 
disastrous results following an explosion. The water-tube boiler, 
on the other hand, is safe, and suited to higher pressures, but in 
some cases requires greater manual labor in operation. 

Advantages. Before discussing these boilers in detail, let us 
consider briefly the salient points. 

Safety. Probably the greatest advantage claimed for the 
water-tube boiler is its safety. The boiler contains much less 
water than does the flue or tubular boiler, and the water is divided 



TYPES OF BOILERS 



41 



into small masses, thus minimizing serious results in case of rupture. 
On account of the shape and arrangement of parts, the circulation 
is usually good, and no part exposed to the fire can be uncovered 
while there is a reasonable quantity of water in the boiler. 

Rapidity in Raising Steam. The many small streams into 
which the water is divided as it passes through the furnace greatly 
facilitate the absorption of heat. Because of the small streams 
and the rapid circulation, the water is converted into steam in a 
relatively short time. Several hours, usually 5 to 7, are required 
to raise steam to working pressure in a tubular boiler, while in 
many water-tube boilers steam can be raised to over 200 pounds 
pressure in less than half an hour. 

Durability. Most water-tube boilers are so designed that no 
seams are exposed to the fire or hot gases. Seams are the weakest 
part of a boiler and, as strains due to unequal expansion concentrate 
at such points, leaks, or even ruptures, are liable to occur if seams 
are exposed to the fire. In the water-tube boiler, the joints between 
tubes and tube sheets are not in the direct path of the hot gases. 

Loss of Heat. The loss of heat will evidently be reduced to a 
minimum if the heating surface is clean and thin. The small diam- 
eter of the water tubes (2 to 4 inches) allows the use of thin metal 
which does not hinder the transmission of heat. The rapid circu- 
lation in the water-tube boiler prevents the accumulation of sedi- 
ment, which is a poor conductor of heat. Still further, dust and 
dirt do not readily collect on the 
convex surface of water tubes, 
but the inside of fire tubes soon 
becomes choked with soot unless 
cleaned frequently, Fig. 40. It 
will be noted that the fire-tube 
type offers no choice as to the 
manner the gases are presented 
to the heating surface; they must 
pass through the tube longitudi- 
nally, while in water-tube boilers the gases may be forced to travel 
longitudinally with the tubes or compelled to cross them transversely. 

Less Weight. It is a well-known fact that a cylinder of large 
diameter must be much thicker than one of small diameter when 




i^Er m$ti$ & 




Fig. 40. 



Collection of Soot in Fire-Tube and 
Water-Tube Boilers 



42 TYPES OF BOILERS 

the internal pressure is the same. The thickness of the shell of a 
fire-tube stationary boiler is not excessive, because of the moderate 
diameter; but in the return-tubular marine boiler, the shell plates for 
250 pounds pressure would be about If inches thick. The difficulty 
of working such thick plates and their great weight render the 
cylindrical boiler unsuitable for high pressures. The small tubes 
and drums of the water-tube boiler may be made quite thin even 
for very high pressures. In general, it may be said that, for the 
same capacity and pressure, the weight of a water-tube boiler is 
only about two-thirds that of a fire-tube. 

Classification. Many attempts have been made to classify 
water-tube boilers. By some writers a classification based on 
circulation, or on the principle of operation, is claimed to be superior 
to any division according to construction. 

On page 4 of this article is given a classification according to 
features of construction. No classification is altogether satisfactory 
because boilers overlap into other divisions; a water-tube boiler 
may be sectional, of the double-tube type, have horizontal tubes, 
straight tubes, and free circulation. In order to have some sort of 
classification, and as no discussion will be entered into regarding 
relative merits, the classification given will be here adopted and 
followed as closely as conditions will permit. 

Water-tube boilers are divided into two great classes — hori- 
zontal and vertical. Under these heads come sectional and non- 
sectional, straight-tube and curved-tube, and single-tube and 
double-tube. If the tubes are nearly horizontal, such as is the case 
of the Babcock and Wilcox, Edge Moor, Heine, and others, the 
boiler will be called horizontal; if the tubes are vertical, or nearly 
so, as in the Wickes, Stirling, etc., the boiler will be classed as vertical. 

Although most boilers can be classified as already outlined, 
there are a few of such peculiar construction and arrangement that 
they must be placed by themselves under "Peculiar Forms". 

As it is impossible to discuss all makes of boilers, a few repre- 
sentative forms will be considered as types of their respective classes. 
No attempt will be made to choose any make as being the best, 
because many conditions must be considered in selecting a boiler. 
The boilers described, except in a few cases, are now used extensively 
in either stationary or marine work. 



TYPES OF BOILERS 



43 



HORIZONTAL TYPES 

Babcock and Wilcox. Water Tabes Nearly Horizontal — Steam 
and Water Drum Horizontal — Straight- Tube — Single- Tube — Sec- 
tional. This boiler consists of a large number of 4-inch tubes, 18 




Fig. 41. Vertical-Header Longitudinal Drum B. & W. Boiler Equipped with B. & W. Super- 
heater and Chain Grate Stoker 
Courtesy of Babcock and Wilcox Company, Xew York City 

feet long, connected to one another and to a horizontal steam and 
water drum. The arrangement of the parts is shown in Fig. 41, 
which is a side view of a much-used form of this boiler. 



44 



TYPES OF BOILERS 



Each tube is expanded into a header of the form shown in Fig. 42. 

The tubes in a vertical row enter one piece, and this vertical row- 
is independent of the others, thus 
making it a sectional boiler, with a 
"staggered" arrangement of the 
tubes. In the back side of the 
front header, and in the front side 
of the rear header, holes are drilled 
into which the w y ater tubes are 
expanded. In the front side of the 
header opposite each tube is a 
handhole fitted with a handhole 
plate. The details of construction 
are shown in Fig. 43. The tops 
of the headers are connected to the 
steam and water drum by short 
tubes, and the same construction 
is used for connecting the mud 
drum to the rear header. 

Operation. The grate is at the 
front end of the boiler under the 
higher end of the tubes. The hot 
gases from the fire are guided by 
division plates and bridges, so that 

after rising from the grate they pass up between the tubes; the 

gases then pass downward among the tubes and, after rising a second 

time, pass off to the chimney. In this way, the direction of the 

currents of hot gases is at all times 

almost at right angles to the tubes, thus 

impinging upon them instead of passing 

parallel to the heating surfaces, as in 

the case of fire tubes. As the gases 

impinge three times against the stag- 
gered tubes, the heating surface is very 

efficient. 

Circulation. The feed water enters 

the steam and water drum through the pipe shown in Fig. 44. 

It is thus heated before it mixes with the hot water in the boiler. 







Fig. 42. 



Wrought-Steel Vertical Header for 
B. & W. Boiler 




Fig. 43. Handhole Fittings for 
B. & W. Boiler 



TYPES OF BOILERS 



45 



As the water in the tubes becomes heated, it rises to the higher end, 
where it is partly converted into steam; a column of water and 
steam rises through the header to the drum, in which the steam and 
water become separated. The cooler water at the rear of the steam 
and water drum flows down into the lower end of the tubes and, 
as it becomes heated, rises. Thus there is a continuous circulation. 




Fig. 44. Partial Vertical Section Showing Method of 
Introducing Feed Water in B. & W. Boiler 

Steam is taken from the rear end of the steam and water drum. 
Much of the soft scale-forming matter and mud falls to the mud 
drum, from which it can be blown out. 

This boiler is manufactured with both cast-iron headers and 
forged-steel headers; with round or elliptical outside handhole plates 
setting on machine surfaced seats and held by steel safety clamps 
on the inside; and with inside handhole cover plates of elliptical 



46 



TYPES OF BOILERS 



form. The forged-steel header boilers are used for the higher 
pressures. The marine form of this boiler has a cross drum; that is, 
the drum is at right angles to the tubes instead of parallel to them. 
It is similar in form to the cross-drum types used for stationary 
work. This form is used in case there is not sufficient head room. 

Root. Tubes Nearly Horizontal — Drums Horizontal — Straight- 
Tube — Sectional. This brief outline indicates that the Root water- 







Fig. 45. Section of Root Water-Tube Boiler 
Courtesy of Abendroth and Root Manufacturing Company 

tube boiler is, in its main features, like the Babcock and Wilcox. In 
fact, the difference is in detail of construction only. Fig. 45 shows 
a longitudinal section of the boiler. Surrounding the tubes is the 
steam and water drum which has attached to the under side, near 
the front end, a cross box having openings on its face to receive the 
regular connecting bends from the top row of tubes. 

Construction. The Root water-tube boiler is composed of 
4-inch tubes. These tubes are expanded into cast-iron headers as 



TYPES OF BOILERS 



47 



shown in A, Fig. 46. A vertical section is formed by placing one 
pair upon another as shown -at B, Fig. 46. One tube of each pair is 
connected to one above it by a flexible bend, by means of which 
an uninterrupted circulation from the bottom to the top of the 
section is obtained. A metallic packing ring, C, D, and E, Fig. 46, 
insures a tight joint between the bend and the header. 

To form the boiler several 
of these vertical sections are 
placed side by side. The theory 
is that these vertical rows are 
not to be rigidly connected 
because the lower tubes, being 
nearer the fire, expand more 
than those above. 

Circulation. Each section 
is connected to the cross box of 
the overhead drum into which 
the water and steam are dis- 
charged from the tubes. At the 
rear of the boiler a plate is riv- 
eted to the drum and bored to 
receive the tubes that make the 
connection between the drum 
and rear headers. The feed 
water enters at the top of the 
mud drum, upon which the rear 
ends of the tubes rest (see Fig. 
45), and meets the hot water 
coming from above. The circu- 
lating water then flows from the top of the mua drum into the 
lower end of the tubes. As these tubes are surrounded by hot 
gases, the water becomes heated and rises through the tubes to the 
steam and water drums. This heated water contains bubbles of 
steam which leave the water and collect in the steam drum. The 
water flows back through the steam and water drum and descends 
through the back header to meet the entering feed water. The 
water level is kept at about the middle of the steam and water 
drums. 




Fig. 46. Root Boiler Tube and Header Details 



TYPES OF BOILERS 49 

The hot gases from the fire pass among the tubes three times in 
practically the same manner as in the Babcock and Wilcox boiler. 

Worthington. Tubes Nearly Horizontal — Drums Horizontal — 
Straight- Tube — Sectional. This form of boiler is much the same in 
principle and operation as the Babcock and Wilcox boiler, but the 
parts are differently proportioned and arranged, Fig. 47. The fur- 
nace extends under the entire boiler, and the tubes are set over it 
close together in oppositely inclined series. No flame walls or 
baffle plates are used. 

Construction. Boilers up to 125 h. p. are usually made to fire 
at the end as shown in Fig. 47, in which the tubes extend across the 
furnace from front to back, and the steam and water drum is at 
right angles to the tubes as shown in the cross section. The tubes 
of each vertical row are expanded into straight headers which 
contain seven or eight tubes. Opposite each tube is a handhole. 
These headers are arranged close together, forming the boiler 
enclosure. 

Circulation. The feed water enters the steam and water drum 
and the circulation carries it down through pipes running to the 
lower headers and from thence into the mud drums as shown. 
From the mud drum it rises through the inclined tubes over the fire 
into the upper headers. The w r ater now containing bubbles of 
steam enters the steam and water drum by means of short tubes 
shown in Fig. 47. 

The covering for this boiler is an iron casing, no brick being 
used except to enclose or line the furnace. 

Edge Moor. Tubes Nearly Horizontal — Drums Horizontal — 
Straight- Tube — Non-Sectional. The Edge Moor water-tube boiler 
differs from those previously discussed among the water-tube class 
in this respect, that the tubes, instead of being expanded into sec- 
tions, are expanded into box-shaped headers w T hich are large enough 
to include all of the water tubes. The tubes are always 4 inches in 
diameter and usually 18 feet long, though they may vary from this 
length. 

Construction. Fig. 48 illustrates the general form of construc- 
tion; this same figure shows how superheating surface is added, the 
latter being shown by the loops located between the drums and the 
tubes. 



50 



TYPES OF BOILERS 



Fig. 49 shows clearly how the headers are connected with the 
drums in such a manner as to avoid the construction of a "throat" 
through which the steam and water must pass after leaving the 
tubes in their circulation through the boilers. This is a distinctive 




Fig. 48. Edge Moor Boiler Showing Superheaters. Boiler Construction is Standard; 

Setting Special 
Courtesy of Edge Moor Iron Company, Edge Moor, Delaware 

feature of the Edge Moor boiler. Note that the drums do not project 
through the headers. 

Fig. 50 shows the flanged handholes opposite each tube end and 
the elliptical cover plate, which, on account of its shape, is inter- 






TYPES OF BOILERS 



51 




Fig. 49. 



Header and Drum Connections in Edge 
Moor Boiler 



changeable and, with the aid of a gasket, carries the boiler pressure 
so as to hold the plate to its seat. This construction is unique on 
account of the flanging fea- 
ture and, because the metal 
is retained between the hand- 
hole openings, permits desir- 
able tube spacing opposite 
with the assurance that there 
is ample strength in the 
handhole sheet. The stays 
across the header are usually 
solid. 

Circulation and Opera- 
tion. The circulation of 
steam and water is identical 
with that previously de- 
scribed for the Babcock and 
Wilcox boiler. The aim of the construction is to provide as little 
internal resistance to circulation as possible by the removal of 
obstructions. In setting features this boiler has been installed in a 
great variety of ways; the normal large boiler is usually similar to 
that of the Babcock and Wilcox 
shown in Fig. 41 ; in special in- 
stances as shown in Fig. 48; and 
for the smaller sizes as shown in 
Fig. 52. 

Heine. Tubes Nearly Hor- 
izontal — Drums Parallel to Tubes 
— Straight- Tube — Non-Sectional. 
The Heine water-tube boiler is not 
a sectional boiler. Instead of being 
expanded into small headers 
grouped to form a boiler, all the 
tubes, which are 3| inches in diam- 
eter, are expanded into the inside 
plates of a water leg at each end. 

Construction. The construction of this water leg is shown in 
Fig. 51. It is composed of two parallel plates flanged and riveted 




Fig. 50, 



Arrangement of Elliptical Flanged 
Handholes of Edge Moor Boiler 



52 



TYPES OF BOILERS 



to a butt strap. The plates are strengthened by short hollow screw 
stays similar to those used in the water-leg construction of fire- 
box boilers. At the top, the water leg is curved and joined to the 
steam and water drum by riveting. Opposite each tube is a circular 
handhole for cleaning the tube, or replacing it if defective. 

Circulation. The feed water enters at the front of the steam 
and water drum, Fig. 52, and flows into the mud drum, a small 
drum shown at the rear of the steam and water drum. From here 
it passes to the rear header with much less velocity. The water 
is warmed while passing through the pipe leading to the mud drum, 
and as it flows slowly through the mud drum it deposits its sedi- 
ment. The accumulated sed- 
iment is blown off by means 
of the blow-off pipe at the 
rear. The water, as it be- 
comes heated in the mud 
drum, rises and passes to the 
front of the mud drum, from 
which it flows in a thin sheet 
to the rear of the steam and 
water drum and to the rear 
water leg. From the rear 
water leg it enters the tubes, 
in which it is partly con- 
verted into steam. The mixture of steam and water enters the 
higher end of the drum from the water leg. A deflection plate 
prevents water from being carried to the perforated steam pipe 
shown at the highest point of the drum. 

The flow of hot gases from the fire is directed by tile placed on 
the top and bottom rows of tubes as shown in Fig. 52. The hot 
gases flow nearly parallel with the tubes instead of across them as 
in the Babcock and Wilcox and in the Edge Moor boilers. 

Mosher. Tubes Nearly Horizontal — Drums (Cross Type) Hori- 
zontal — Bent-Tube — Non-Sectional. The chief difference between 
this boiler and those already described is that it has short bent 
tubes, thus making a more compact boiler. This type is more often 
used in marine than in stationary work. The boiler consists of a 
large steam and water drum, Fig. 53, connected by slightly curved 




Fig. 51. Heine Boiler Water Leg 



TYPES OF BOILERS 



53 



tubes to a smaller water drum. The steam drum is supported by 
two large circulating pipes, one at each end, which are connected 
by other pipes to the water drum. Thus the circulation is down 
these pipes and along the pipe at the bottom up to the water drum, 
and thence to the steam drum by the tubes which are in contact 
with the hot gases. 

The feed-water heater, or economizer, shown above the main 
drum, consists of two small drums connected by tubes. The paral- 




Fig. 52. Longitudinal Section of Heine Water-Tube Boiler and Setting 
Courtesy of Heine Safety Boiler Company, St. Louis, Missouri 

lei dotted lines in the steam drum show how tubes are removed 
and replaced, a series of openings, which are capped with plugs 
as shown in Fig. 54, being provided in the upper drum for remov- 
ing the tubes. All the tubes in one vertical section pass through 
one opening. Each plug is a conical-headed bolt, having a short 
piece of copper tube, a washer, and a nut. The conical head and 
the copper tube are inserted in the hole until the washer is in con- 
tact with the outer surface of the drum. The nut is then screwed 
up, thereby flaring the end of the copper tubing as shown. The 



54 



TYPES OF BOILERS 





TYPES OF BOILERS 55 

steam pressure on the conical head increases the tightness of the 
joint. 




Fig. 54. Mosher Drum. Plugs 

Thornycroft=Marshall. Tubes Nearly Horizontal — Drums (Cross 
Type) Horizontal — Bent- Tube — Non-Sectional. The Thorny croft - 
Marshall non-sectional boiler consists of a large horizontal steam 
and water drum, a vertical water box or header, and the gener- 
ating tubes. Like the Mosher, the tubes are bent slightly, but 
the header is quite different from that boiler. 

Construction. The general features of construction are shown 
in Fig. 55. The steam and water drum, sometimes called the 
separator barrel, is simply a cylinder with dished ends. The water 
is carried at about one-third the height of the cylinder. The tubes, 
which are 3f inches in diameter, are connected in pairs to a 
junction box at one end and to a water box or header at the other 
end. Thus each pair forms a unit, but the two tubes of the unit 
are not in the same vertical plane. The upper tube enters the 
header as high as possible and the lower ones enter low down, 
thus giving considerable upward slope. From near the top of 
the water box, three rows of tubes lead to the separator barrel 
as shown in Fig. 56. The water box is simple in construction, 
the flat plates being stayed by short hollow screw stay bolts. 
The junction boxes are not restrained in any way; this construc- 
tion, combined with the slight curve of the tubes, allows free 
expansion. 

Circulation. The feed water enters the steam and water drum 
and then passes to the water box through the two lower sets of 
tubes, Fig. 55. The water enters the lower ends of the various 
pairs of tubes, as shown in Fig. 56, and rises in the tubes while in 
contact with the hot gases from the furnace. The mixture of 
steam and hot water then enters the header, from which it passes 
to the steam and water drum by means of the highest row of 



56 



TYPES OF BOILERS 



tubes. The difference in height of the two tubes of a unit insures 
good circulation. A baffle plate prevents the water from splashing 
to the steam pipe. 




Fig. 55. Vertical Section of Thornycroft-Marshall Boiler 



The hot gases pass upward among the tubes which cross so 
frequently that the heating surface is quite efficient. 

Niclausse. Tubes Nearly Horizontal — Drum Horizontal — 
Straight- Tube — Sectional This boiler differs essentially from those 
already described in that it is of the double-tube type. In general, 



TYPES OF BOILERS 



57 



it consists of a number of elements which form a vertical header, to 
which tubes are connected. The tubes are set at an angle of about 
6 degrees to the horizontal. Above the elements is a transverse 
steam and water drum which is in communication with the headers. 
The general arrangement of parts is shown in Fig. 57. 

Construction. The interesting feature of this type of boiler 
is the arrangement of the tubes and headers. To increase the 
circulation the principle of the "Field" tube is employed. In this 
construction the outer or generating tubes, 3j inches in diameter, 
are closed at one end. Each generating tube contains an inner 




Fig. 56. Diagram Showing Circulation in Thornycroft- 
Marehall Boiler 



circulating tube which is l^f inches in diameter, open at both ends. 
The closed ends of the generating tubes are supported by being 
placed in holes in a plate or rack at the rear of the boiler. The 
forward end of the circulating tube is attached to a cap which screws 
into the outer end of the generating tube. A recess in this cap 
provides a bearing for an arch bar which spans two tubes, keeps 
them in place, and is itself secured by a nut on a bolt which, in turn, 
is screwed into the header, Fig. 58. 

The front end of the generating tubes is of peculiar shape. To 
allow the water to enter the circulating tubes, and to fasten the 
tubes to the header without expanding them, each generating tube 



58 



TYPES OF BOILERS 




Fig. 57. Vertical Section of Niclausse Water-Tube Boiler 



TYPES OF BOILERS 59 

is provided at the open end with two cone-shaped parts; these are 
about 8 inches apart. The first cone fits into a taper hole flanged 
outward in the front face of the header, and the second cone fits 
a similar hole in the rear face of the header. Both the holes 
and tubes are ground to the same size and taper. About midway 
between the cones, a third expanded portion occupies the tube hole 
in the diaphragm or middle plate of the header, Fig. 58. The 
portion of the tube within the header is called the "lantern". At 
this point the tube is cut away so that water may freely enter the 
tube, the openings being above and below. In Fig. 58, the upper 
tube is in its normal position, but the lower tube has been turned 
through 90 degrees to show the construction. 




Fig. 5S. Niclausse Boiler Details 

To stand high steam pressures, the elements of the headers 
are made of wrought steel and are sinuous in shape. Fig. 59 shows 
the shape of the header and the positions of the tubes. Each ele- 
ment contains 24 tubes in two vertical rows of 12 each. In the 
middle of the headers, there is a diaphragm for dividing the interior. 
The front passage serves as a "downcomer" for the water, and the 
rear is the "upcomer", or riser, for the mixture of steam and 
water. 

The lower ends of the headers are closed, and the upper ends 
flanged to connect with the steam and water drum, which is 42 
inches in diameter. 

Circulation. Fig. 58 gives an idea of the direction of circula- 
tion. Water from the drum descends in the front compartment 
of the header, flows into the circulating tubes, which communicate 



60 



TYPES OF BOILERS 



with the front compartment only, and, after flowing the length of 
the circulating tubes, enters the generating tubes. The water then 
comes back through the annular spaces in the generating tubes to 
the rear compartment of the header, because the generating tubes 
communicate with the rear compartment only, while in the annular 

space it is partly evaporated. 
M 1 \-M The mixture of steam and water 

then rises to the drum. 

VERTICAL TYPES 

Wickes. Water Tubes Ver- 
tical — Straight-Tube — Non-Sec- 
tional. Let us now consider a 
water-tube boiler having vertical 
tubes. Fig. 60 shows the general 
arrangement of the parts of the 
Wickes vertical water-tube boiler. 
At the top is a cylindrical steam 
and water drum into which the 
upper ends of the vertical tubes 
are expanded. At the bottom is 
a cylindrical drum of the same 
diameter as the upper drum. The 
tubes are straight and plumb 
when in position; they are ar- 
ranged in parallel rows with a 
clear space between rows to 
admit a small hoe to remove any 
soot that may accumulate on the 
tube sheet of the lower drum. 
The tubes are' divided into two compartments by heavy fire- 
brick tile. The tubes in the section adjacent to the furnace are 
called "risers"; those in the rear are the "downcomers", because the 
heated water rises to the steam drum through the front tubes, and 
the cooler water flows down those in the rear. The feed w^ater is 
introduced into the upper drum. The direction of flow of hot 
gases is the same as that of the water. 

The furnace is extended in front of the boiler setting and built 




Niclausse Header Details 



TYPES OF BOILERS 61 

entirely of brick. The hot gases from the fire come in contact 
with the tubes without passing through a combustion chamber, 
unless special furnace construction is adopted. 




Fig. 60. Section of Wickes Vertical Water-Tube Boiler 
Courtesy of Wickes Boiler Company, Saginaw, Michigan 

Cahall. Annular Steam and Water Drum — Tubes Vertical — 
Straight- Tube — Single- Tube — Non-Sectional. The Cahall vertical 
water-tube boiler consists of an annular steam and water drum, a 
cylindrical lower drum, and 4-inch vertical tubes connecting these 
two drums. An external circulating pipe also connects the two 



52 



TYPES OP BOILERS 




Fig. 61. Cahall Vertical Water-Tube Boner, Showing Longitudinal Section of Setting Enclosing 

a Traveling Grate 



TYPES OF BOILERS 63 

drums. As this pipe is filled with comparatively cool water and 
the generating tubes with a mixture of hot water and steam, the 
circulation is up in the 4-inch tubes and down in the external pipe. 
The feed water enters the steam and water drum, flows down the 
external pipe to the lower drum, and then rises in the generating 
tubes to the steam and water drum. 

The fire is in a brick furnace in front of the boiler, as shown in 
Fig. 61, the hot gases rising among the tubes. The annular form 
of the steam drum makes the central space conical; in this space 
several deflecting plates, or baffles, cause the hot gases to remain 
among the tubes. After heating the water in the tubes, the hot 
gases pass through the opening in the steam and water 
drum, coming in contact with the metal containing the steam. 
This thoroughly dries the steam and in many cases slightly super- 
heats it. 

Both the steam drum and the lower drum are equipped with 
swinging manheads. The steam drum also has several handholes 
for use in removing and replacing tubes. 

Stirling. Tubes Nearly Vertical — Drums Horizontal — Bent- 
Tube — Non-Sectional. The Stirling boiler, shown in Fig. 62, con- 
sists of three cylindrical steam and w^ater drums at the top and a 
mud drum at the bottom. The lower drum is connected to the 
upper drums by three sets of tubes which are curved slightly at the 
ends. The curved tubes allow for expansion and make it possible 
to have the tubes enter the drums radially. 

The feed water enters the rear steam and water drum and, 
coming in contact with the hot gases just before they enter the 
uptake, becomes gradually warmed. This heating causes most of 
the sediment to fall to the mud drum, from which it may be blown 
out at intervals. The mud drum is protected from the intense heat 
of the furnace by the bridge wall. 

Each set of tubes is separated from the others by partition 
walls or baffles of fire-brick tile, so that the gases from the furnace 
pass along the entire length among the first set of tubes; they are 
then guided downward among the second set of tubes, and, after 
rising again among the tubes of the third set, escape to the chimney. 
The fire-brick arch just above the furnace insures an even distri- 
bution of the gases and promotes combustion; the arch heats the 



64 



TYPES OF BOILERS 



entering air to a high temperature, thus reducing the danger of 
chilling the tubes by an inrush of cold air. 

Steam is taken from the middle drum, which is set a little 




Fig. 62. Longitudinal Section of Stirling Boiler, Showing Setting and Mechanical Stoker 
Courtesy of Babcock and Wilcox Company, New York City 

higher than the others in order to obtain more steam space. The 
boiler is surrounded on the rear and two sides by the brick setting; 
the front is of cast iron or of pressed steel. Numerous openings in 
the brickwork allow entrance for cleaning. 




TYPES OF BOILERS 



65 



This type of boiler is flexible and adapted to cramped places, 
as it can be made broad with little height or high with small floor 
area. All parts are either cylindrical or spherical in shape and of 
wrought metal. The curved tubes reduce the strains resulting 
from unequal expansion and contraction. 




Fig. 63. Vertical Section of Rust Water-Tube Boiler 
Courtesy of Babcock and Wilcox Company, New York City 

Rust. The Rust water-tube boiler, manufactured by the Bab- 
cock and 'Wilcox Company, is intended to include the advantages of 
boilers made up of drums and tubes only, thus getting away from 
the disadvantages of header construction and many handholes, and 
at the same time avoiding the use of bent tubes. To accomplish 



66 



TYPES OF BOILERS 




Fig. 64. 



Section Showing How Rust Boiler Tubes 
are Set into Drum 



this the vertical boiler illustrated in Fig. 63 is made up of straight 
tubes and four drums, with the exception of two rows of vertical 
tubes and the circulating tubes connecting the two upper drums, 
which are bent. The purpose of the two rows of bent tubes in the 
middle section is to provide a stable support for the baffle wall. 
When superheaters are used they are located with the elements pro- 
jecting almost up to the top 
rear drum, close to the mid- 
dle baffle wall in the space 
between the bent tubes and 
the straight tubes. 

In order that the tubes 
may be inserted into their 
holes normal to the surface of the drums, the drum sheets are 
forged hot in a hydraulic press fitted with special dies, the effect of 
this forging being shown in Fig. 64. 

Bigelow=Hornsby. The development of the Bigelow-Hornsby 
boiler is an attempt to satisfy the demand for large boiler capacity 
without resorting to the double- and triple-deck boiler-house design. 
A section consists of four tube units suspended from structural iron 
overhead and connected by short tubes to a central steam drum as 
shown in Fig. 65. As the main steam drum is the only rigid mem- 
ber, expansion and contraction are easily taken care of, no matter 
how many sections are used or how long the central drum is made. 
The boilers rate at 125 horsepower per section, so that a boiler of 
1250 horsepower has ten sections. The water circulation is down 
the rear units and up the front as well as in the individual units 
themselves. The feed water enters the top rear unit drums and 
mixes with the downward circulating currents, thus providing that 
the coldest water shall meet the coldest gases. On account of the 
open structure of the boiler, it is an easy matter to inspect and 
clean it. As the tubes are perfectly straight, one can look through 
them and see if they need cleaning. The baffle-plate arrangement is 
shown in Fig. 65, the tile being placed at the back of each unit 
between the successive sections, thus making the hot gases pass 
through the tubes of the forward unit to the second and so on. 
When used, a superheater is placed below the main steam drum. 
This boiler is developed from the Hornsby, an English type. 



TYPES OF BOILERS 



67 




Fig. 



65. Section of Hand-Fired Bigelow-Hornsby Vertical Boiler 
Courtesy of The Bigelow Company, New York City 



68 



TYPES OF BOILERS 



Connelly. Tubes at Various Pitches — Drums Horizontal — 
Bent- Tube — Single- Tube — Non-Sectional. The Connelly boiler, 
shown in Fig. 66, consists normally of two cylindrical steam and 
water drums and one water drum at the top, all three of which 
connect with a mud drum at the bottom. When the units are 
built especially large, this boiler may consist of as many as seven 



- ±Y?s8£:s~ros 

- %£ /?EO BfZlCK 



/VpA=7V^y/_ V\f77Vpg 







Fig. 66. Connelly Water-Tube Boiler 
Courtesy of D. Connelly Boiler Company, Cleveland, Ohio 

drums arranged by uniting two boilers of the four-drum type into 
one pressure unit, the place of articulation being the front top 
water drum of each, thereby permitting the rejection of one of 
these drums. In any of the boilers of this general design all the 
tubes are bent to the required shapes so as to enter the drums 
radially. 



TYPES OF BOILERS 69 

Circulation. The feed water enters the rear top drum, which 
is also the place from which steam is taken. Normal water 
circulation carries the new water from the rear top drum down to 
the mud drum, from which it rise£ to either the top front or 
middle drum. Steam separation occurs in the middle top drum, 
from w^hich it passes by means of bent connecting tubes to the 
rear top drum. 

The spacing is such as to permit the removal of any tube 
without disturbing the rest. While the boiler is baffled in several 
different ways, the standard form is shown in the illustration. 
Particular attention is called to the facilities provided for admitting 
a portion of the traveling hot gases to the chamber formed by the 
circulating tubes leading from the middle drum to the rear drum. 
The expectation is that heat will be delivered to the steam, caus- 
ing it to be slightly superheated. It is suggested that this boiler 
be studied in comparison with the Stirling boiler illustrated in 
Fig. 62. 

Erie City. Tubes Vertical — Drums Horizontal — Bent- Tube — 
Non-Sectional. The Erie City vertical water-tube boiler, illus- 
trated in Fig. 67, consists of one upper steam and water drum 
communicating by means of bent tubes to a bottom mud drum. 
In ordinary sizes, the tubes are arranged in three banks — 
four rows in the front two banks 'and three rows in the rear 
bank. 

Circulation. The water is fed in the center of the lower mud 
drum, rising in the front banks of tubes to the top drum, where 
entrained steam bubbles are separated. The cylindrical shell of 
the top drum is longer than that of the mud drum, the additional 
length being devoted to two internal steam compartments over 
which the ends of the dry pipe project so as to remove, as far 
as possible, the steam outlet of the boiler from the places of most 
violent ebullition. 

Two baffles are constructed to cause the gases to follow the 
heating surface. The first baffle is built from the lower drum to 
within a few feet of *the top drum, leaning upon the back row of 
tubes of the first bank. The second baffle extends from the upper 
drum to within a short distance of the lower drum. This arrange- 
ment combined with the setting walls compels the hot gases to 



70 



TYPES OF BOILERS 



traverse the heating surface in three passages, the outlet being at 
the top rear of the setting. 




Fig. 67. Erie City Vertical Water-Tube Boiler. Brick Setting Incomplete, 

Baffles not Inserted 

Courtesy of Erie City Iron Works, Erie, Pennsylvania 

The tubes are independently removable, the spacing being 
so arranged. Also they are bent in such a form as to enter the 
drums radially. 



TYPES OF BOILERS 



71 




Fig. 68. vertical Section of Hazelton Porcupine Boiler and Setting 



72 



TYPES OF BOILERS 



PECULIAR FORMS 

Hazelton or Porcupine. Tubes Horizontal — Drum Vertical — 
Straight- Tube. The Hazelton water-tube boiler differs in many 
respects from the boilers thus far described. Like most water-tube 
boilers it consists of a steam and water drum and water tubes, but 
the central standpipe is vertical and the short horizontal tubes 
radiate from the central drum. According to our classification it 
is not a vertical water-tube boiler because the tubes are horizontal; 
also, it is not a horizontal boiler, as in general appearance it is vertical. 




( ( ( ( <r 



« ( < 



< JQoooooooob O O OOQOOOOOOO 



D C 

>oc 



X^Z) 



T 



) ) )) 



Fig. 69. Part Section of Porcupine Boiler Showing Center Tubes 

The grate is circular and formed around the central drum, 
which rests on a circular cast-iron foundation. Above the grate, 
the central drum forms part of the heating surface and is the steam 
reservoir; below the grate it is the mud drum, which may be entered 
by means of a manhole just below the grate. As shown in Fig. 68, 
the standpipe above the fire is provided with radial tubes. The 
arrangement of these tubes gives the boiler the name "Porcupine". 

The standpipe is about 3 feet in diameter for large boilers. The 
tubes are about 4 inches in diameter, and project out from the 



TYPES QF BOILERS 



r;3 



standpipe about 2\ feet, the number varying with the size of the 
boiler. The outer ends of the tubes are closed and hemispherical, 
and the inner ends expanded into the standpipe. The tubes are 
free to expand and contract without bringing any stress on the 
boiler. 

Steam is taken from the top of the central drum. To get dry 
steam, small pipes are inserted as shown in Fig. 69. The steam 
passes up into the small tube at the top of the standpipe and then 
through the small pipes to the ends of the generating tubes. It 




Fig. 70. Harrison Safety Boiler. A Type no Longer Manufactured but Still Used 
Courtesy Harrison Safety Boiler Works, Philadelphia 

then flows back through the generating tubes to the annular space, 
and thence to the steam pipe. The feed pipe enters the mud drum 
and extends upward nearly to the water line; it then returns nearly 
to the level of the grate, terminating in a spraying nozzle. 

This type of boiler may be enclosed in a brick setting, as shown 
in Fig. 68, or by a sheet-steel covering lined with fire brick. 

Harrison. Sectional — Hollow Cast-iron Spheres Instead cf 
Tabes. All boilers thus far described have employed tubes as a 
means of dividing the water into small masses in order to make the 
heating surfaces more effective. In the Harrison safety boiler, Fig. 



74 TYPES OP BOILERS 

70, tubes are not used; instead, the water is contained in hollow 
cast-iron spheres, called units. These units, Fig. 71, are arranged 
in vertical rows, called slabs, which are suspended side by side, 
about one inch apart, from an iron framework. The brickwork 
setting is merely a covering to keep the hot gases in contact with 
the units. 

The use of units in place of tubes combines great strength and 
a large heating surface. They are strong because small and spher- 
ical, and, on account of the division of the water into small masses, 
the heating surface is effective. The units are held together by 
long bolts which pass through 
the centers, as shown in Fig. 

71. The machined faces 
make a steam-tight joint 
without packing. This boiler 
requires the same fittings as 
other boilers 

The great advantage of 
this boiler is safety. From 
the construction, it is appar- 
ent that rupture cannot ex- 
tend beyond the unit; thus disastrous explosions cannot occur. They 
are claimed to be durable, economical, rapid steamers, and easily 
handled. The capacity can be increased by merely adding more slabs. 

MARINE BOILER TYPES 

Elements of Design. Because boilers used in marine work must 
be built to meet the special conditions imposed by the construction 
of the ships containing them, and because boiler practice is slightly 
different at sea than on land, it is thought best to point out the 
main features of design encountered in marine boilers, grouping 
them together in one part of this article so as to distinguish them 
as a class, even though all of them must classify among the 
different groups according to form, as, for instance, "fire-tube", 
"water-tube", etc. The principles governing the construction 
of marine boilers cannot be different from those governing the 
construction of all other boilers, and whatever differences are shown 




Fig. 71. Details of Harrison Boiler Units 



TYPES OF BOILERS 75 

come from the restrictions imposed by the spaces into which the 
boilers must go, and because of the attempt to reduce fire hazard. 
Marine boilers usually take one of the following forms: 

(1) Rectangular, or box boilers 

(2) Cylindrical, or drum boilers 

(3) Water-tube boilers 

As was pointed out with respect to boilers used in stationary 
plants, the tendency is toward the greater use of water-tube boilers 
on account of their greater safety under high pressures, and because 
they are somewhat more compact for a given horsepower. It will 
be seen, also, that the internally-fired type of boiler, which at one 
time supplanted nearly every other form of marine boiler, presents 
the difficulty of offering very limited facilities in the matter of grate 
surface; and this one fact has contributed not a little to the adop- 
tion of water-tube boilers in their stead. From these remarks it 
must not be inferred that cylindrical boilers are not now frequently 
used in marine work; they are still the most common boilers on 
board ship, but the newer vessels, and especially the larger ones, 
are being equipped with water-tube boilers built particularly for 
marine use. 

RECTANGULAR MARINE FIRE=TUBE BOILERS 

Features of Construction. The rectangular boiler, Fig. 72, is 
made square or box-shaped; hence the sides are flat. This form 
was one of the earliest used; at present, however, its use is restricted 
to low pressure, that is, under 30 pounds per square inch. The 
reason why this boiler cannot be used for high pressure is because 
the flat plates tend to bulge outward when under high pressure. 
In order to prevent the plates from bulging, they must be stayed with 
numerous longitudinal and vertical stay rods. 

Box boilers are generally made with an internal uptake, as 
shown in Fig. 72. This construction makes possible a larger steam 
space and reduces loss of heat by radiation. It is, however, expen- 
sive in first cost and repairs; also, the plates of the uptake waste 
rapidly, especially near the water line, because the heat is not trans- 
mitted as readily by steam as by water. In case the uptake is 
made separate and does not form a part of the boiler, this objection 
is avoided. 



76 



TYPES OF BOILERS 



The tubes of the rectangular boiler are usually horizontal, or 
nearly so. When set inclined or with a "rake", as it is called, there 
is more room for manholes at the smoke-box end. The extremities 
of the tubes at the combustion chamber end are near the furnace, 
but are higher at the smoke-box end. The water level is about the 
same as with the horizontal tubes, the ends nearest the combustion 
chamber having the greater depth of water over them. The inclina- 
tion is about 1 inch to the foot. 




Fig. 72. Wet-Bottom Rectangular Marine Boiler 



Wet= and Dry=Bottom Boilers. Rectangular boilers are made 
in two ways, and from the form of construction are known as "wet 
bottom" and "dry bottom". Wet-bottom boilers are made with the 
furnace wholly inside and independent of the shell, the furnaces 
being surrounded by water on all sides. The wet-bottom boiler is 
very difficult to inspect and repair. 

In the dry-bottom boiler, the furnaces terminate in the boiler 
shell at the bottom, having a water space called the water leg 



TYPES OF BOILERS 77 

between them. This water leg causes trouble by getting filled up 
with sediment. The furnace has w^ater around the sides but, like the 
locomotive and most vertical boilers, there is no water underneath. 
The dry-bottom boiler is lighter, as the bottom plates are omitted, is 
cheaper, has greater durablity, and is easier to examine. On the other 
hand, it is more dangerous to the ship, as the heat is likely to cause 
corrosion of the frames if of iron or burn the frames if of wood. 
In order to avoid the large number of stays in the steam space 
for pressures over 30 pounds per square inch, an oval-shaped 
boiler was introduced. It had a semicylindrical top and bottom 
and flat sides. This form was soon abandoned because it would 
stand only about 45 pounds pressure. 

CYLINDRICAL MARINE FIRE=TUBE BOILERS 

The cylindrical boiler succeeded the oval boiler. This boiler 
is made with the shell a complete cylinder. It is lighter, cheaper, 
and more easily made than the rectangular. It occupies more 
space and for a given heating and grate surface, has a smaller 
steam space. Cylindrical or Scotch boilers may be divided into 
three classes, as follows: 

(1) Single-ended boilers 

(2) Double-ended boilers 

(3) Gunboat or through-tube boilers 

For a detailed description of single-ended cylindrical boilers of 
the single-flue type see pages 23 and 24 and Fig. 21. Multiple-flue 
boilers are described on page 25 and shown by Figs. 22 and 23. 
Double-ended boilers are described on pages 25 and 27, and an 
excellent illustration of a multiple-flue boiler of this type is given 
by Fig. 24. Through-tube boilers are described on page 29 and 
illustrated by Fig. 27. 

Locomotive Boiler. The locomotive boiler is used for launches 
and torpedo boats. It is a convenient form and a very light boiler 
for the heating surface. Forced draft is almost invariably used 
with it on account of the small grate area. The furnace crown, 
being flat, requires careful staying. 

MARINE WATER=TUBE BOILERS 
Comparison with Cylindrical Type. For many years the cylin- 
drical boiler was almost the only type used in marine work, and 



78 TYPES OF BOILERS 

for that reason it attained a high state of perfection. From time 
to time, engineers tried to introduce water-tube boilers in place of 
the cylindrical, but on account of poor design, faulty construction, 
or bad management, the experiments were not entirely successful. 
At the present time, however, an increase of speed is demanded 
and, consequently, higher pressures and lighter machinery are neces- 
sary. With this increase of pressure comes increase of weight, 
cost, and damage in case of explosion, if the cylindrical form of 
boiler is retained. Engineers have foreseen that the cylindrical 
boiler must give way to the steam generator which is lighter, 
stronger, and safer. 

A water-tube boiler, if well designed and well constructed, 
seems to fulfill the requirements. Although the cylindrical boiler 
is serviceable, efficient, and can be made to stand any reasonable 
pressure, yet the water-tube boiler possesses many advantages 
over it. 

The principal objections to the cylindrical boiler are the great 
weight, thick plates, difficulty of moving it into and out of vessels, 
and its small furnace space. This last disadvantage has already 
been discussed. Also, when the cylindrical boiler is under forced 
draft, the time allowed for the products of combustion to give up 
their heat is short. 

Among the advantages of this boiler may be mentioned econ- 
omy and steadiness in supplying dry steam, and in this respect it 
excels the water-tube boiler. It is also far better suited for salt 
water than is the water-tube boiler, but this is not a great advan- 
tage at the present time. 

Classification. Water-tube boilers are built in a great variety 
of designs. They may be divided into different classes, as straight 
tube and curved tube; or the drowned tube, that is, those having 
the upper ends submerged, and those having the upper ends open- 
ing into the steam space; or those having a steam drum and those 
having none. 

For convenience let us divide them into two classes, straight 
and curved tube. In the first class we may place, among others, 
the Almy, Belleville, Babcock & Wilcox, Heine, Yarrow, D'Allest, 
and Niclausse. A few of those having curved tubes are the Thorny- 
croft, Normand, Mosher, and Ward. Some of these have been 



TYPES OF BOILERS 



79 






discussed in the preceding pages. Only a few of these boilers need 
be described here, the purpose being to show the manner in which 
ordinary land practice must be modified to conform with the 
requirements for marine use. 




Fig. 73. Sectional Model of Babcock and Wilcox Marine Water-Tube Boiler 

Courtesy of The Babcock & Wilcox Company, New York City 

Babcock & Wilcox Marine Water=Tube Boiler. In Fig. 73 
is shown a sectional view of a model of a marine type of the 
Babcock & Wilcox boiler, looking from a rear position toward 
the firing end. All the essential features of this boiler are clearly 
shown, there being set up for purposes of the illustration two com- 
plete sections united with the end of a steam and water drum. 



SO TYPES OF BOILERS 

Attention is called particularly to the forged-steel rectangular- 
shaped boxes, inclined at the same angle as the tubes, lying along- 
side the grate surface and communicating with vertical forged-steel 
headers. With the exception of the bottom row of tubes and the 
circulating tubes above, it is customary to employ small diameter 
tubes expanded into forged-steel serpentine headers in groups of 
four. Each handhole communicates with a group of four tubes, 
the idea being to avoid the use of a multiplicity of handhole caps. 

It will be noted that the transverse method of baffling is 
employed, but that the low end of the boiler is located in front. 
The bottom row of tubes supports tube tile projecting upward 
from the inner end of which is the first cross-flame plate encoun- 
tered by the gases. The gas outlet is at the top front immediately 
behind the cross-drum. The boiler is enclosed within a steel 
casing lined with fire brick, and the whole constitutes a very com- 
pact economical boiler. To prevent harmful galvanic action and, 
consequently, internal corrosion, it is customary to install zinc 
plates with positive metallic contact between these plates and the 
iron attached to the steam baffle plate within the boiler drum. 
The plan is to employ an electropositive metal which will receive 
corrosion attack in preference to the metal of the boiler when 
galvanic action takes place. Even though such action ceases after 
a few hours of operation, it is important to employ zinc as a 
protection against corrosion owing to the presence of air in the 
feed water. 

Standard Water=Tube Boiler, U.S. Wooden Steamships. In 
order to expedite the building of boilers for the United States 
emergency fleet, the U.S. Shipping Board Emergency Fleet Cor- 
poration, having charge of the building of the ships for the 
Shipping Board, designed the boiler illustrated by Fig. 74. This is 
like the Babcock & Wilcox marine previously dealt with in being 
a straight-tube cross-drum boiler but differs from it in several 
important particulars. The scheme of design is such as to permit 
the construction of the boiler in any well equipped shop, making 
it possible for a relatively large number of boiler manufacturers to 
engage in production rather than confining the output to the 
capacities of a few boiler shops only. It was the preservation of 
this production feature which led to the selection of a "box header" 



TYPES OF BOILERS 



81 




82 TYPES OF BOILERS? 

construction instead of the sectional type, which in turn influenced 
the design by the selection of tube sizes and spacing to fit. 

The system of baffling is longitudinal instead of transverse, 
dead spaces within the tube region being avoided by gaps in the 
baffle placements where normally they would meet the header tube 
sheets. To accommodate the baffles, full spaces are created by 
leaving out horizontal rows of tubes where they would occur in the 
cross-baffled type. Also, the tube width of the boilers becomes 
narrower as the top of the header is approached, the general shape 
of the back header being as shown in the right-hand view, which 
illustrates a front half elevation of the front header within its 
enclosing steel casing. Thus there are 38 3-inch tubes in the 
lowest and only 24 in the highest full rows of tubes. 

The standard boiler has a total heating surface of about 
2500 square feet and 77.5 square feet of grate surface and is 
designed to withstand a working pressure of 200 pounds gage when 
complying with all the rules and regulations of the U. S. Steamboat 
Inspection Service applying to marine water-tube boilers for ocean 
and coastwise trade. Among special features it may be mentioned 
that the cover plates closing the holes opposite each tube are 
conical steel plugs, held in place by cup-shaped yoke plates and 
forged-steel nuts screwed upon threaded stems. The joints are 
made tight by means of copper ferrules, the inner edges of the 
handholes being rolled with a special expander to allow flaring of 
the copper ferrules. The plates therefore receive the pressure 
which tends to close the handhole openings, thus relieving the plate 
stem of the pressure load. 

These boilers are equipped with the customary complement of 
fittings and trimmings suitable for marine practice and are fully 
steel encased outside of fire-brick lining. 

Almy Water=Tube Boiler. In Fig. 75 is shown a front view 
of an Almy marine boiler, with its outside casing, grates, and 
fittings removed. It will be noted that the boiler is made up of 
straight malleable-iron tubes, connected by special fittings with 
one another and with manifolds at the bottom and top terminals. 
The sections that extend along the side from the bottom manifolds 
to the side top manifolds form a loop extending over above the 
fire so as to form the roof of the fire box. The sections arising 



TYPES OF BOILERS 



83 



from the rear bottom manifold form two loops, finally entering at 
the top front manifold. A flat continuous coil extending over the 
entire top is a heater section. The front top manifold is connected 
to a vertical steam dome, or separator, the lower end of which is 
riveted to a horizontal water reservoir extending across the front 
of the boiler. The steam connections are made at the top of the 
separator, while the water reservoir is connected by down flow 
pipes to the ends of the bottom manifolds in front. 




Fig. 75. Almy Sectional Water-Tube Boiler 
Courtesy of Almy Water-Tube Boiler Company, Providence, Rhode Island 

No baffling is placed inside the heating surface, the expecta- 
tion being that the heated gases will envelop the tubes throughout. 
The particular characteristic of the boiler is the very large per- 
centage of the heating surface that is in direct line with the 
radiant heat coming from the fire. 

Double-Tube Type. This boiler is also made in what is known 
as the double-tube type, the expression in this case meaning that a 
double row of tubes following the same general contour is employed 
in place of one tube as shown in the illustration. This expression 



84 TYPES OF BOILERS 

"double-tube" must not be confused with that employed elsewhere 
in this book where one tube is placed inside another. 

Variations from Standard Land Types. The variations from 
standard land types of water-tube boilers are mainly those con- 
cerned with length of tubes and the use of cross-drums instead of 
longitudinal drums. Because the tubes are shorter they may be 
of smaller diameter as well, and the use of cross-drums is also 
permissible for the same reason. 

Grate Area. The grate area is determined in a similar manner 
to that used in designing cylindrical boilers; but for most types the 
area must be greater, so that the heat may be distributed evenly 
over the surface of the tubes. It is not well to have the heat too 
intense near any of the tubes. The construction of most water- 
tube boilers allows some space above the fire for combustion. 

Steam Drum. The size of the steam drum depends upon the 
amount of steam generated by the boiler. In order to make it as 
small and as light as possible, the boilers are sometimes worked at 
high pressure, and the pressure maintained constant at the engine 
by means of a reducing valve. 

Water-tube boilers having the upper ends of the tubes opening 
into the steam space have dash plates and internal steam pipes 
which separate the water and steam. 

Advantages over Cylindrical Type. Water-tube boilers have 
the following advantages over cylindrical boilers: 

(1) Lighter (weight about one-half that of the cylindrical). 

(2) First cost less on account of less material used. 

(3) Less danger of damage in case of explosion. 

(4) Large grate area and large furnace volume for combustion. 

(5) Greater rapidity in raising steam. 

(6) More easily placed aboard or removed. 

(7) Have a larger capacity range. 

The last three conditions are of great importance in the navy. 
As to the relative economy, there is much difference of opinion as 
the conditions vary considerably. In general, the economy is 
about equal in both types. 

The ease of making repairs depends upon the type of boiler. 
The sectional type can usually be repaired more readily than 
others. 



TYPES OF BOILERS 85 

Disadvantages. These boilers have several disadvantages, 
among which may be mentioned the following: 

(1) Tendency to prime. 

(2) Difficulty of feeding. 

(3) Sensitiveness to corrosion and dirt. 

(4) Difficulty of repairing tubes. 

These defects are reduced to a minimum if the boiler is of 
good design, well managed, and constructed of the best material. 

Launch Boilers. The boilers used in torpedo boats, yachts, 
and launches should be safe, light, compact, and economical. Also, 
they should be capable of supplying dry steam at high pressures. 
Small vertical fire-tube boilers are sometimes used, but the water- 
tube boiler is better adapted to this work. The water-tube boilers 
already described are built in small sizes and generally give satis- 
faction. Perhaps the boilers most used for fast launches, yachts, 
and small vessels are the Ward and Mosher. These boilers are 
similar in general principles to most marine water-tube boilers but 
are made small, light, and compact. 

BOILER DESIGN 

FEATURES OF INDIVIDUAL BOILERS 

As the advantages of employing high pressure and superheated 
steam became increasingly apparent and the sizes of the steam- 
using equipments became larger, boiler designers were compelled to 
exercise greater ingenuity and skill not only in order to create 
structures that would meet the two requirements just stated but 
also to overcome other difficulties created out of the means taken 
to afford larger and higher-pressure boiler units. As steam engi- 
neering became better understood, such features as internal cir- 
culation, effectiveness of heating surface, accessibility, repair or 
replacement facilities, sizes and shapes of tubes, etc., demanded 
closer attention. 'Without attempting to lay down all of the con- 
siderations in these several topics, it is believed well to illustrate 
and explain by typical examples the purposes aimed at by different 

designers. 

CIRCULATION 

Fire=Tube Boilers. The horizontal tubular boiler, illustrated in 

Figs, 11, 12, 13, and 14, being the most common of our fire-tube 



86 TYPES OF BOILERS ' 

boilers, will serve as an example of the class with many fire tubes, 
and the considerations entering into its design will apply with 
equal force to the Scotch marine boiler illustrated in Figs. 21 to 25, 
inclusive. Where a large number of tubes are distributed through 
a boiler shell, it is now customary to locate the tubes so as to form 
wider lanes for the movement of steam and water than would 
prevail were the tube spacing uniform throughout. It is more 
important to provide these larger lanes for water travel in the case 
of internally fired boilers built after the pattern of the Scotch 
marines than in the case of horizontal tubular boilers. Experience 
teaches that unless such precautions are taken a definite water 
circulation is not set up and the tendency is to create dead zones 
within the water space, particularly in a boiler like the Scotch marine, 
which does not have hot gases impinging upon the outside shell. 
Fig. 23 shows plainly how extra spaces are provided between tube 
rows. While the primary reason for the spacing shown is to permit 
the construction of the combustion chambers in the rear, it is 
fortunate for circulation that they exist. 

Water=Tube Boilers. Overcoming Resistance to Water Flow. 
The circulation within water-tube boilers constitutes one of the 
most important problems which they present, modern tendencies 
not only causing designers to avoid restrictions as much as appears 
to be necessary but also inducing them to afford positive circula- 
tion by inclining the tubes to a greater extent than at first would 
seem to be required. To illustrate this it is well to point out the 
precautions taken in two boilers of the horizontal water-tube type, 
representing the extremes of sectional and box-header construction. 
In Fig. 44 is shown in vertical section that portion of the B & W 
boiler which is likely to set up the greatest resistance to water flow. 
It will be noted that short 4-inch nipples connect the several 
vertical header sections to the boiler drum proper. In the illustra- 
tion, twelve tubes of 4-inch diameter deliver the water passing 
through them through one 4-inch submerged nipple at the front 
throat; longer 4-inch tubes provide the facilities for keeping the 
boiler tubes supplied with water coming from the rear end of the 
drum. Manifestly, the flow of water, supposing it all to be solid, 
through the nipples must be twelve times as rapid as the average 
flow through any single tube. Turn now to Figs. 48, 49, and 50, 



TYPES OF BOILERS 87 

In these are shown the details of construction of Edge Moor 
boilers in the particular place known as the throat and previously 
dealt with in B & W boilers. In this instance no nipples are 
employed. The depth of the w^ater leg is about 1 foot; then, 
supposing the Edge Moor boiler is also twelve tubes high, the 
space available for water movement on the way to the drums is an 
area of about 78 square inches as against about 12 square inches 
for the B & W boiler. There is this difference between the two 
boilers : the B & W boiler is pitched 2\ inches to the linear foot, 
whereas the Edge Moor boiler tube pitch is 1 inch to the foot; 
consequently, while the B & W boiler may set up a greater 
resistance to circulation, it also provides what is believed to be a 
correspondingly greater force to overcome it. 

Prevention of Moisture. Some types of boilers, mainly the 
vertical or semivertical, provide extraordinarily large circulation 
facilities and sometimes do so to such an extent that the space into 
which the tubes discharge may be in a constant condition of very 
active ebullition. If the water tends to foam, this violent stirring 
accentuates the trouble and additional means must be provided to 
afford space and time for the water thrown up into the steam 
space to settle back to the general level. Baffles are provided to 
receive water and steam impingement, thereby causing the water 
to lose its velocity while the steam may pass to an additional drum 
for further separation. The Stirling boiler, Fig. 62, is a good example 
of this arrangement. 

Auxiliary Circulating Pipes. It is sometimes necessary to 
provide special circulating pipes leading from one drum to another 
or from the upper steam drum to a lower water drum, as in Fig. 61. 
This is done because all the tubes of the boiler are intended to 
carry water and steam upward to the steam drum, thereby afford- 
ing no way for the water to reach the lower drum except by 
setting up a counter-circulation resisting that set up by heat trans- 
mission. To facilitate the circulation, therefore, the pipe column 
shown on the left of the illustration is installed and all downward 
movement of water may take place through this. 

Importance of Qood Circulation. Features of Boilers Affected. 
In general, the matter of circulation affects two of the most 
important features of boilers. If the circulation is inadequate, it is 



88 TYPES OF BOILERS 

reflected in the inability of the boiler to absorb heat readily and, 
fully as important as this, in the material curtailment of the life of 
the parts subjected to heat. This is due to the fact that steam 
pockets are created on the water side of the heating surface and, 
in as much as steam is a poor absorber of heat as compared with 
water, the plates will not transmit the heat to the steam as rapidly 
as though solid wetness were presented to the plate; hence the 
metal may become overheated. If the circulation is such as to 
permit the alternate but rapid formation of steam pockets followed 
by solid wetness, fatigue of the metal is set up and crystallization 
ensues. The deterioration under such circumstances is very rapid. 
Retirement of Old Forms. It is this one matter of insufficient 
circulation that has caused in modern boiler practice the retirement 
of many of the old forms which formerly were well received. 
Where a high rate of duty is expected regardless of what the 
character of water may be, a boiler such as that illustrated in 
Fig. 68 is out of the question. The same comment can be made 
with reference to Fig. 70, even supposing the materials would with- 
stand modern high pressure and in other respects be satisfactory. 

EFFECTIVENESS OF HEATING SURFACES 

Heating Surface Problem Difficult. Manifestly no good pur- 
pose is served by providing useless heating surface, yet the prob- 
lem of using all the heating surface provided is not as simple as 
it may appear. Out of the accumulated experience of boiler build- 
ers, designers, and users has come a fairly good understanding of 
what are the main items to be considered in employing the heating 
surface properly so that injury in some other particular may not 
be encountered. Referring to Fig. 41, it will be noted that 
the boiler is baffled by the placement of two vertical flame 
plates located transverse to the tubes. It is recognized in this 
instance that possibly the upper portion of the top rows of tubes 
near the front headers may not be well employed as heating 
surface. The same remark applies to a less extent to the bottom 
rows of tubes in the second and third gas passes. Were expedients 
adopted to employ these tubes throughout their length to their 
fullest extent, then so much resistance to the draft forces would be 
set up that the furnace end of the installation might suffer. It is 



TYPES OF BOILERS 89 

true also that the advantage of having gases leave the boiler set- 
ting near the top rear influences the design of setting. In the 
special setting shown in Fig. 48 the attempt is made to utilize 
the heating surface more effectively by the employment of four 
passes instead of three. The design undoubtedly accomplishes 
this purpose but does so at the expense of creating a materially 
larger draft loss in the boiler-tube region as compared with a more 
open system of baffling, which effect, being foreseen, is met by 
using longer tubes than normally as well as by providing greater 
chimney or fan draft facilities. 

Designers of settings do not all agree as to the means that 
should be taken to accomplish the same effect. The inclined 
baffle tile and baffle ledges leaning against or adjacent to the tube 
banks of the boiler shown in Fig. 63, are manifestly installed to 
cause the gases to travel closely within the tube regions. The 
boiler illustrated in Fig. 67, not having such ledge baffles permits 
the gases to seek the lanes not filled with tubes. 

In Fig. 61 is illustrated a design that may become ineffective 
on account of the failure of parts. In this case the two conical 
baffle rings placed within the center tube cone may burn out, 
thereby allowing the gases to pass directly to the chimney without 
further encountering heating surface. 

Where the gases have an opportunity to accept a choice of 
paths, it is seldom possible to make all the heating surface effective, 
but it is important to avoid two or more paths which the gases may 
take through the heating surface on their way to the chimney. 

Refer now to Fig. 52. If this boiler is so designed on account 
of space considerations that it becomes relatively high in number of 
tubes and narrow, then the vertical distance between the upper 
and lower baffles is too liberal for the gases generated in the fur- 
nace and the tendency is for them to travel across the tube chamber 
without coming into intimate contact with the tubes throughout 
their length. Such a boiler is faulty in tube arrangement, yet 
the design may be amply strong and good in all other particulars. 

The effectiveness of heating surface is often destroyed by the 
creation of pockets within the tube chambers in which large 
quantities of soot and fine ashes may accumulate without being 
readily displaced. Such a trouble is accentuated by the fact that, 



90 TYPES OF BOILERS 

when a pocket exists, gas circulation within the pocket is of low 
velocity and the means taken for the blowing out of soot becomes 
ineffective because the gases, moving slowly, permit the soot to fall 
back after being stirred up. In other words, there is no special 
difficulty in removing soot where the gases travel with high velocities, 
but it is almost impossible to remove it unless there is a swift-moving 
current to carry it after it has been dislodged. 

Absorbtion of Heat by Radiation. The most effective heating 
surface that can be obtained is that which is in the direct line of 
radiant heat coming from the fuel bed. It is this peculiarity of 
the heating surface of the externally fired shell boiler that has 
retained this type in such general use as to constitute for moderate 
pressures the most common boiler met with. In this instance the 
boiler shell is located immediately above the fire and the trans- 
mission of heat through the relatively thick shell metal, even when 
internal circulation is not especially good, is very rapid. Fire-box 
boilers are a still more striking example of the rapidity of radiant 
heat absorption. Those boilers of the water-tube type that present 
large quantities of heating surface to the radiant heat action of 
fires are invariably more economical steamers than those which 
are not so liberally provided with heating surface within range 
of radiant heat. Unfortunately the very causes of a high rate of 
radiant heat transmission sometimes set up difficulties in other 
particulars, among which may be mentioned the likelihood of 
forming steam pockets due to faulty circulation, w T hich in turn may 
cause tube failures to an excessive degree. 

ACCESSIBILITY 

Provisions Usual for Inspection and Cleaning. Under this 
topic the main problems are those of the plant designer rather 
than of the boiler designer. There are practically no manufac- 
turers of special boiler equipment that do not provide facilities for 
internal cleaning or inspection of pressure parts. The facilities 
may be crude or require much effort to employ them, but they are 
present. It is important in selecting a boiler to look into these 
matters and, if a choice is permitted, to select the ones wherein 
the least manual labor is required during operation. An important 
instance is that of choosing for water-tube boilers the kind of a 



TYPES OF BOILERS 91 

handhole cover plate which does not depend too much upon the 
skill of the operator to make a tight joint when closed. In other 
words, it is advantageous to select a plate that has the pressure 
of the steam forcing it against its seat rather than the reverse, 
not only to reduce the hazard but to reduce the labor and time 
out of service. 

In general, cover plates should be selected that have their 
pressure loads symmetrically distributed. Odd shaped plates 
requiring complicated forms of gaskets should be avoided, unless 
some very decided advantage in some other particular is created 
by their use. 

It is usually less trouble to remove one manhole plate giving 
access to a whole bank of tubes than to take off as many plates 
as there are tubes. This is not always an advantage, as the mere 
taking off of the plate does not complete 'the job and as in most 
instances where a manhole plate is taken off in order to make the 
tubes accessible a man must enter the drum, which imposes the 
further necessity that the drum be cool and free enough from 
vapor to permit him to enter to perform his work. 

Replacement of Tubes. Facilities in Boiler Itself. It is impor- 
tant that any part which may fail, such as a boiler tube, be 
removed and replaced without disturbing too many other boiler 
elements. The Stirling boiler is an example of one where tube 
placing is such that even the most remote or interior tube can be 
passed out from its nest without getting down other tubes. The 
practice of so designing boilers is becoming quite general and is 
to be commended unless carried so far that the gases do not have 
a fair attack at the heating surface. 

Space Facilities. In designing or installing a boiler the only 
safe assumption is that any one of the tube elements may fail and 
require replacement. For this reason not only must the boiler 
permit having its tubes replaced but spaces surrounding the 
boiler must also be provided. For instance, a straight-tube boiler 
like the horizontal water-tube types will require a space in one 
direction, either front or back, equal to the length of the tubes. 
The same remark applies to any of the fire-tube boilers, such as 
the horizontal tubular and the Scotch marines. To replace the 
tubes, the boiler illustrated in Fig. 47 must have a space covering 



92 TYPES OF BOILERS 

a rather large horizontal area. Some forms of vertical boilers 
require almost double the installation height in order to replace 
tubes without wrecking the boiler setting. 

SHAPES>ND SIZES OF TUBES 

Straight vs. Bent Tubes. It is always desirable to retain 
tubes in a straight condition as manufactured instead of bending 
them to some particular shape, since the user need not carry in 
reserve a number of different shapes and it is also easier to inspect 
and clean them. It does not follow, however, that a bent-tube 
boiler is necessarily less to be desired than a straight-tube boiler, 
for it is more than likely that the bent-tube boiler may be better 
able to accommodate itself to the space in which it is to be 
located. 

Tube Diameters. Fire- Tube Boilers. In the matter of tube 
diameters there is less freedom of choice than as to shape. If the 
boiler is of the fire-tube type, then the diameter of the tube plays 
an important part in the matter of draft reduction. The loco- 
motive boiler is a good instance of the use of tubes of small 
diameter being made possible by exceedingly high draft created 
at the exhaust nozzle. If the attempt were made to apply 
locomotive tube practice to stationary practice it would be found 
impractical because the tubes would be too small, would rapidly 
clog up with soot, and even when clean would impose too much of 
a restriction. In general, the longer the fire tube, the larger its 
diameter needs to be. 

Water- Tube Boilers. In water-tube practice, tubes of small 
diameters are not suitable in that the application of intense heat 
tends to create steam pockets within them, because the circulation 
forces cannot overcome the water flow resistance. Tube failures 
due to overheating, fatigue, or scale formation may combine to 
make their cost prohibitive. 

It is a fair statement that the greater the rate at which the 
boiler-heating surface is expected to operate the larger should 
water tubes be; also, the longer the tubes the larger the diameter. 
The reverse is partially true with respect to fire tubes, and in this 
instance the practical limitations are those set up by the avail- 
able draft. 



TYPES OF BOILERS 93 

PLANT FEATURES INFLUENCING BOILER DESIGN 

Analysis of Problem. While it is impossible to take note of 
the many items that must be considered in the problem of design- 
ing steam generating plants, it is not out of place to indicate 
briefly the salient considerations. In presenting a few of the most 
vital elements of boiler plant design the most intimate association 
of the several topics or divisions of the subject is presupposed, it 
being inevitable that the elements of water, fuel, steam demand, 
etc., are closely interrelated so far as influencing the type and size 
of boiler units is concerned. 

As a fundamental truth it may be stated that all types of 
boilers that have withstood the test of time service can, in general, 
be made to give practically the same economy of service, provided 
the features external to them are selected with good judgment. 
By external features are meant tight settings, good boiler water, 
adequate draft, etc. 

Personal Element. The reader must, however, bear in mind 
that whatever the intention of the designing engineer the perform- 
ance of the equipment depends upon the one person or group of 
persons who operate it. In other words, a prime requisite is that 
the equipment shall be of such a character that the labor service 
available is able to grasp the possibilities offered by the plant; 
therefore, if the plant steam output demand is not large enough to 
warrant the engagement of highly skilled operating engineering, 
then, of course, it shows decidedly poor judgment to select equip- 
ment of a nature effective only with expert manipulation. 

Size of Plant. Where the steam demand requires the installa- 
tion of more than one unit, the problem is sometimes quite diffi- 
cult. In general, it is usually not good practice to select two units 
instead of three of the same aggregate rating. On the other hand, 
it is not as economical, either as to first cost or later operation, to 
select many small units in place of a relatively few large ones. 
Where a choice is permitted, the plant designer should aim to 
provide an additional stand-by unit or the space in which one may 
be placed. In the latter event, provision should be made to per- 
mit the addition of the breeching and other boiler room facilities 
without disturbing the character of the original installation. 



94 TYPES OF BOILERS 

Stokers. The size of the boiler units as well as their number 
determine the feasibility of installing stokers. The latter are not 
usually serviceable or economical when combined with boilers of 
less than 150 horsepower. Some types of stokers do not become 
economically worth while until the sizes both of the units and of 
the plant as a whole become quite large, the character of labor 
required for operation and their cost being against the use of the 
most refined stokers unless the plant has a large output. The 
nature of the available fuel determines the type of stoker that can 
be used economically and by learning the economical size of the 
stoker of that type in common practice the plant designer may 
come to fix upon boiler sizes somewhat different than he would 
select if not considering stokers. If stokers are justified by other 
considerations, the boiler design must be made to fit, by which is 
meant that the dimensions of boilers of any given make may vary 
to suit furnace size and shape. Also, the boiler baffling may 
require modification to get satisfactory results. 

Water. One of the troublesome elements in many cases is the 
character of water that is available for plant use. If the water 
precipitates a very hard scale, then it is usually best to treat it 
before admitting it to the boiler, but even with such precautions 
there are occasions when some scale will appear. If the scale so 
formed cannot be completely eliminated by treatment, the engineer 
is likely to be justified in ruling against the adoption of water-tube 
boilers, though, no matter what the type of boiler, scale of this 
character is likely to cause trouble. Or, he may be justified in 
rejecting a water-tube boiler in which the labor of making the 
tubes accessible for cleaning is much greater than in a boiler of 
another type; for instance, he may choose a vertical or semi- 
vertical water-tube boiler in place of a horizontal water-tube boiler 
having a multiplicity of handhole plates. It is to be said, however, 
that unless the water contains common salt in solution there is 
hardly any reason why water treatment will not permit the greatest 
freedom in the selection of the type of boiler. Where the available 
water is unsatisfactory, a water-treating equipment of good design is 
always a paying investment, no matter what type of boiler is selected. 

Fuel. Aside from grate sizes and character, it is extremely 
important that the nature of the available fuel be considered in 



TYPES OF BOILERS 95 

connection with the type of boiler selected. In the most favorable 
furnaces, soot or fine ash is bound to develop at the grate and 
pass to the heating surface where large portions may deposit. 
Since dirty heating surface on the fire side is more costly in fuel 
than any other form of boiler uncleanliness, if the fuel itself 
contains a relatively large percentage of volatile or soot-making 
matter, then the engineer should select a type of boiler in which 
the places of soot lodgment are easily accessible. For instance, a 
three-crosspass horizontal water-tube boiler affords less opportunity 
for soot deposit in the tube chambers than a horizontal boiler with 
horizontal passes. In any event, soot removing demands close 
study in all stages of the boiler plant design, consideration being 
given to the furnace, the boiler passages, and the spaces around 
the boiler settings, keeping in mind that the nature of the coal has 
a direct bearing on the amount of such deposits. Thus the kind 
of fuel determines to a large extent the kind of stoking or firing 
equipment which, in turn, fixes the size and shape of the boiler. 
Available Space. Aside from the very obvious necessity of 
choosing boiler units that may be installed within the space 
assigned to them, there are less obvious factors that need considera- 
tion. The fact that an installation may be made does not argue 
that it is necessarily good, as is attested by the thousands of 
instances where sacrifices to space considerations were made in the 
first instance for unimportant reasons. If it is remembered that a 
boiler is only an absorber of heat and that there is also the prob- 
lem of heat generation, little difficulty is encountered in understand- 
ing the reasons for the following points: 

(1) Under no circumstances compromise with the question 
of providing combustion time and space. If the head room is 
cramped, make it up by selecting a type of boiler that gives at 
least ample horizontal room. A reverse situation demands oppo- 
site treatment. 

(2) Sufficient draft combined with furnace design determines 
the rate at which the fuel may be burned as well as the economy 
of heat evolution. A boiler design that does not lend itself to 
the chosen space without sound breeching design should be 
rejected. Linked up with this is the whole subject of boiler 
baffling. When designing a new plant create (by overprovision, 
if possible), all the draft intensity that may be desired. If looking 



96 TYPES OF BOILERS 

for trouble in an existing plant, it will probably be found by an 
analysis of the draft facilities. The sizes of gas passages and their 
relative positions and shapes are among the important items. 

(3) Do not overlook tube replacement facilities. 

(4) Soot removal, whether done manually or by permanent 
blowers, demands adequate alley ways around boiler settings. 
Many forms of stokers require side inspection and manipulating 
space. No other condition is so disagreeable as cramped quarters 
for routine boiler and furnace operation. In order to get adequate 
space it may be necessary to reduce setting widths and increase 
boiler heights when choosing them, but it is usually worth while 
to do so unless some other important feature is adversely affected. 

(5) It is a mistake to install more than two boilers in a 
single setting, and, where done by choice, the reasons for so doing 
should be of the best and it should be fully appreciated that 
sacrifices will be made during the life of the plant. 

(6) Many boilers properly designed as to pressure parts fail 
to be fully effective because of faulty supports, poor baffles, 
improper expansion provisions, etc., all of which are reflected in 
the creation of cracks in settings attended by uneconomical heat 
absorbtion, reduced capacity, and high furnace maintenance costs. 
This part of the subject warrants the closest study in even the 
most minute details. 



INDEX 



INDEX 



PART PAGE 

A 

Accessibility of boiler parts II, 90 

provisions for inspection and cleaning II, 90 

replacement of tubes II, 91 

Almy boiler II, 82 

Annealing I, 16 

Auxiliary circulating pipes II, 87 

B 

Babcock and Wilcox boiler II, 43, 79 

Belpaire boiler II, 31 

Bigelow-Hornsby boiler II, 66 

Blow-off pipe II, 2 

Boiler accessories II, 1 

blow-off pipe II, 2 

brackets II, 2 

breeching II, 2 

chimneys II, 2 

columns II, 2 

damper II, 2 

feed pump II, 1 

furnace fittings II, 2 

fusible plugs II, 2 

gage cocks II, 1 

handholes II, 2 

heaters II, 2 

high- and low-water alarms II, 2 

injector II, 1 

lugs II, 2 

manholes II, 2 

masonry II, 2 

pressure gage II, 2 

safety valve II, 2 

steam piping II, 2 

tools II, 2 

water gage II, 1 

Boiler action, essential principles of I, 1 

Boiler construction I, 1-58 

allowable pressure I, 56 

area of grate I, 52 

calking I, 25 

expanding tubes, methods of I, 47 

flanging , I, 19 

flues I, 42 



2 INDEX 

PART PAGE 

Boiler construction (continued) 

furnace flues I, 49, 57 

heating surface I, 55 

manholes I, 33 

materials I, 2 

plates and joints, arrangement of I, 27 

rating I, 53 

requirements I, 50 

riveted joints ' I, 15, 20 

sections I, 57 

shaping butt straps I, 19 

stays I, 34 

steam space I, 54 

tubes I, 42 

water-leg construction I, 28 

welded joints I, 26 

Boiler design II, 85 

features of individual boilers II, 85 

accessibility II, 90 

circulation II, 85 

effectiveness of heating surfaces II, 88 

shapes and sizes of tubes II, 92 

plant features II, 93 

analysis of problem II, 93 

available space II, 95 

fuel II, 94 

personal element II, 93 

size of plant II, 93 

stokers II, 94 

water II, 94 

Boiler function ; II, 1 

Boiler inspection during manufacture I, 57 

Boiler materials I, 2 

brass I, 4 

bronze I, 4 

cast iron I, 2 

copper I, 4 

steel I, 3 

tests of I, 4 

diagrams I, 6 

elastic limit I, 5 

elongation I, 5 

reduction of area I, 5 

rules of American Society of Mechanical Engineers I, 8 

standard regulations I, 8 

strain I, 5 

stress I, 4 

stretch limit I, 5 

testing machines I, 7 



INDEX 3 

PART PAGE 

Boiler materials (continued) 
tests of 

ultimate strength I, 5 

wrought iron I, 2 

Boiler tubes I, 42; II, 91 

holes and ends I, 46 

methods of expanding I, 47 

Dudgeon I, 48 

Prosser I, 47 

spacing I, 42 

stay I, 48 

types I, 47 

Boiler types II, 1-96 

boiler design II, 85 

classification . II, 3 

early forms II, 5 

fire-box II, 29 

fire-tube II, 29 

internally-fired marine II, 22 

marine II, 74 

modern flue boilers II, 9 

peculiar forms II, 34, 72 

water-tubes II, 39 

Brackets II, 2 

Brady Scotch boiler II, 36 

Brass. .' I, 4 

Breeching II, 2 

Bronze I, 4 



Calking. . I 

proper method I 

tools I 

Cast iron \ I, 

Circulation in boilers II 

auxiliary circulating pipes II 

fire-tube boilers II 

importance of II 

water-tube boilers II 

Cleaning of boiler II 

Cochrane boiler II, 

Connelly boiler .' II, 

Construction of boilers I 

Copper I 

Cornish boiler II, 

Cylindrical boilers II, 

marine II, 



25 

25 

25 

2 

85 

87 

85 

87 

86 

90 

35 

68 

-58 

4 

9 

7 

77 



4 INDEX 

PART PAGE 

D 

Damper frame and damper II, 2 

Directum boilers II, 38 

Double-ended boiler II, 25, 77 

Double-tube boiler, definition of II, 5 

Dudgeon expander I, 48 

E 

Edge Moor boiler II, 49 

Erie City boiler II, 69 

Expanders I, 47 

Externally-fired boiler, definition of II, 5 

F 

Feed pump II, 1 

Fire-box boilers II, 29 

definition of ... II, 5 

Fire-tube boilers II, 5, 14, 85 

circulation in II, 85 

definition of II, 5 

fire-box II, 29 

Belpaire II, 31 

Lentz II, 33 

locomotive II, 29 

stationary II, 34 

Wootten II, 33 

horizontal II, 14 

multitubular , II, 14 

single-flue II, 14 

internally-fired marine II, 22 

return-tubular II, 22 

through-tube II, 29 

peculiar forms II, 34 

Brady II, 36 

Cochrane II, 35 

Directum II, 38 

Shapley II, 35 

vertical II, 18 

Manning II, 20 

single-tube ' . . II, 18 

Flanging I, 19 

Fuel II, 94 

Furnace fittings II, 2 

Furnace flues I, 49, 57 

G 

Gage cocks II, 1 

Galloway boiler II, 12 

Grate area for boilers I, 52 

Gunboat boiler II, 29. 77 



INDEX 5 

PART PAGE 

H 

Handholes I, 34 

Harrison boiler II, 73 

Haystack boiler II, 5 

Hazelton boiler II, 72 

Heater II, 2 

Heating surface of boilers I, 55; II, 88 

Heine boiler II, 51 

High- and low-water alarms II, 2 

Horizontal fire-tube boilers II, 14 

Horizontal water-tube boilers II, 43 

Horsepower of boilers I, 51 

I 

Inspection of boiler I, 57; II, 90 

Internally-fired boiler, definition of II, 5 

Internally-fired marine boiler II, 22 

L 

Lancashire boiler II, 11 

Launch boilers II, 85 

Lentz boiler II, 33 

Locomotive boilers II, 29, 77 

Lugs II, 2 

M 

Manholes I, 33; II, 2 

frame construction I, 33 

location I, 33 

size of opening I, 33 

Manning boiler. II, 20 

Marine boilers II, 74 

cylindrical II, 77 

double-ended Scotch . . II, 77 

gunboat II, 77 

locomotive II, 77 

single-ended II, 77 

rectangular II, 75 

wet- and dry-bottom II, 76 

water-tube II, 77 

Almy II, 82 

Babcock and Wilcox II, 79 

comparison with cylindrical II, 77 

launch II, 85 

Standard, U.S. wooden steamships II, 80 

variations from standard land types II, 84 

Masonry II, 2 

Modern flue boilers II, 9 

Cornish II, 9 



INDEX 



PART PAGE 



Modern flue boilers (continued) 

Galloway II, 12 

Lancashire II, 11 

Mosher boiler II, 52 

Multitubular boiler II, 14, 19 

N 

Niclausse boiler II, 56 

Non-sectional boiler, definition of II, 5 



Plant, size of II, 93 

Plates and joints, arrangement of I, 27 

Porcupine boiler II, 72 

Pressure of boilers I, 56 

Pressure gage II, 2 

47 



Prosser expander. 



I 



R 



Rating of boilers I, 

Reamed holes I, 

Rectangular marine boilers II, 

Return-tubular boilers II 

Return-tubular fire-box boiler II 

Riveted joints in boilers 

annealing 

butt straps 

efficiency 

flanging 

reamed holes 

rivet holes, drilled 

rivet holes, punched 

types of 

butt 

lap 

Rivets 

forms of 

methods of driving 

Root boiler II 



Safety valve II, 2 

Sectional boiler, definition of II, 5 

Sections of boilers I, 57 

Shapley boiler II, 35 

Shop equipment I, 15 

Single-ended boiler II, 23, 25, 77 

Single-flue boiler II, 14, 23 

Single-tube boiler II, 5, 18 

definition of II, 5 



53 
16 
75 
22 
34 
15 
16 
19 
20 
19 
16 
15 
15 
20 
22 
21 

17 

18 
46 



INDEX 7 

PART PAGE 

Space available, factor in boiler design II, 95 

Standard boiler, U.S. wooden steamships H, 80 

Stationary boilers, II, 34 

Stationary return-tubular boiler II, 27 

Stay bolts I, 37 

Stay rods I, 35 

Stays I, 34 

area to be stayed I, 42 

crown sheet supports I, 38 

diagonal I, 36 

gusset I, 36 

load on stay bolts I, 42 

riveted stay bolts I, 37 

stay rod. I, 35 

stiffening angles I, 38 

Steam piping II, 2 

Steam space of boilers I, 54 

Steel I, 3 

Stirling boiler II, 63 

Stokers. II, 94 

T 
Tables 

double-riveted joints, efficiencies of I, 24 

lap-welded boiler tubes, dimensions of I, 46 

riveted lap joints, proportions of I, 22 

rivets, dimensions of I, 18 

stay bolts with V-threads, allowable loads I, 41, 42 

stays and stay bolts, maximum allowable stress I, 41 

steel, chemical composition of I, 3 

Testing boiler steel, rules for I, 8 

Testing machines I, 7 

Thornycroft-Marshall boiler II, 55 

Through-tube boilers II, 29 

Tools II, 2 

Tubes of boilers I, 42; II, 91 

diameter of II, 92 

fire-tube boilers II, 92 

water-tube boilers II, 92 

replacement of II, 91 

straight vs. bent II, 92 

Types of boilers II, 1-96 

Y 

Vertical fire-tube boilers II, 18 

Vertical water-tube boilers II, 60 

W 

Wagon boiler II, 6 

Water II, 94 



8 



INDEX 



Water evaporation per pound of fuel . 

Water-leg construction 

Water-tube boilers 

advantages 

circulation in 

horizontal 

Babcock and Wilcox 

Edge Moor 

Heine 

Mosher 

Niclausse 

Root 

Thorny croft-Marshall 

Worthington 

peculiar forms 

Harrison 

Hazelton or Porcupine 

vertical 

Bigelow-Hornsby 

CahaU 

Connelly 

Erie City 

Rust 

Stirling 

Wickes 

Water-tube marine boilers 

Welded joints 

Wet- and dry-bottom boilers 

Wickes boiler 

Wootten boiler 

Worthington boiler 

Wrought iron 



PAGE 

53 
28 
39, 86 
40 
86 
43 
43 
49 
51 
52 
56 
46 
55 
49 
72 
73 
72 
60 
66 
61 
68 
69 
65 
63 
60 
77 
26 
76 
60 
33 
49 
2 






